当前位置:首页 > 八年级 > 数学试卷

【324048】2024八年级数学下册 专题1.5 二次根式的化简求值专项训练(30道)(含解析)(新

时间:2025-01-15 21:33:56 作者: 字数:11722字
简介:


 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 专题1.5二次根式的化简求值专项训练(30道)

1.(炎陵县期末)已知x3+2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> y3﹣2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,求x2yxy2的值.

【分析】将原式提取公因式进行因式分解,然后代入求值.

【解答】解:原式=xyxy),

x3+2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> y3﹣2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 时,

原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

=(9﹣8×3+2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 3+2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

1×4 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

2.(锦江区校级期末)已知 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,求a2﹣3ab+b2的值.

【分析】先分母有理化得到a <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1b <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1,再计算出a+b2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ab1,接着把a2﹣3ab+b2变形为(a+b2﹣5ab,然后利用整体代入的方法计算.

【解答】解:∵a <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1b <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1

a+b2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ab2﹣11

a2﹣3ab+b2=(a+b2﹣5ab=(2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2﹣5×13

3.(锦江区校级期末)已知 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> b <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

求:(1aba+b的值;

2)求a2+b2+2的值.

【分析】(1)利用平方差公式将ab的值进行二次根式分母有理化计算,然后代入求值;

2)利用完全平方公式将原式进行变形,然后代入求值.

【解答】解:(1a <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

b <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

ab=( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> )( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> )=6﹣51

ab=( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> )﹣( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

原式=abab

1﹣2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

aba+b的值为1﹣2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

2)原式=(ab2+2ab+2

=(2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2+2×1+2

20+2+2

24

a2+b2+2的值为24

4.(西湖区校级期末)已知:y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 5,化简并求 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 的值.

【分析】根据二次根式有意义的条件得到x4,则y5,再利用约分得到原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,然后通分得到原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,最后把xy的值代入计算即可.

【解答】解:∵x﹣4≥04﹣x≥0

x4

y5

原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

=﹣4

5.(东兴区校级期中)已知:ab2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> bc2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

求:(1ac的值;

2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 的值.

【分析】(1)根据二次根式的加法法则计算;

2)根据完全平方公式、提公因式法把原式变形,把已知数据代入计算即可.

【解答】解:(1)∵ab2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> bc2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

ab+bc)=(2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> +2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ),即ac4

2)原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

7

6.(新会区校级期中)化简求值:已知x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,求 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 的值.

【分析】先进行通分,化简后将xy的值代入计算即可.

【解答】解 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 时,

原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2

7.(金山区校级期中)化简并求值: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,其中x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【分析】利用因式分解的方法把原式变形为 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,利用约分得到原式=xy,再把xy的值化简后代入计算即可.

【解答】解:原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

=( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> )•( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

xy

x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1

8.(吉安县模拟)已知x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,求x+yxy的值.

【分析】根据完全平方公式和二次根式的性质对xy进行化简,然后计算它们的和与积.

【解答】解:∵x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>


y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

x+y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

xy=( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> )( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> )=3﹣21

9.(阳新县月考)已知x+y=﹣6xy8,求代数式y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 的值.

【分析】根据加法法则、乘法法则和已知条件得出xy同号,并且都是负数,化简所求式子,代值即可.

【解答】解:∵x+y=﹣6xy8

xy同号,并且都是负数,

y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

=﹣( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

=﹣5 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

10.(双流区月考)(1)已知ab <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,求a <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> b <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 的值;

2)已知x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2,求x2+y2+2xy

【分析】(1)先根据二次根式的性质化简得到原式=a <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> b <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,再进行讨论:当ab都为正数时,原式=2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ;当ab都为负数时,原式=﹣2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,然后把ab <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 分别代入计算即可;

2)先计算出x+y2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,再利用完全平方公式得到x2+y2+2xy=(x+y2,然后利用整体代入的方法计算.

【解答】解:(1a <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> b <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> a <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> b <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

a <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> b <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

ab <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

ab都为正数时,原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 3

ab都为负数时,原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 3

2)∵x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2

x+y2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

x2+y2+2xy=(x+y2=(2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 220

11.(浦东新区期中)已知 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,求 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 的值.

【分析】将原式中分子进行因式分解后再约分化简,然后将已知等式代入,再根据二次根式分母有理化的计算方法进行化简计算.

【解答】解:原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 时,

原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

4

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 的值为4

12.(静安区校级月考)先化简,再求值: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,其中a <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> b <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【分析】将原式除法转化为乘法,然后进行计算,再利用平方差公式对字母a的值进行分母有理化计算,从而代入求值.

【解答】解:原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

a <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 7﹣4 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

a7﹣4 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> b <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 时,

原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

7 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 12

13.(浦东新区校级月考)已知x为奇数,且 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,求 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 的值.

【分析】利用二次根式的性质确定x的取值范围,再利用x为奇数,得出x的值;利用因式分解把要求的式子化简后再代入求值.

【解答】解:∵ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

解得:7≤x9

x为奇数,

x7

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> x+1)• <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

原式=(7+1 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 8×432

14.(鄞州区月考)已知a <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

1)求a2﹣4a+4的值;

2)化简并求值: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【分析】(1)先将a化简,然后通过配方法将原式化简,最后代入a求值.

2)将原式先化简,然后代入a的值求解.

【解答】解:(1a <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

a2﹣4a+4=(a﹣22

a2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 代入(a﹣22得( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 23

2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

=(a﹣1 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

a2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

a﹣11 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 0

原式=a﹣1 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1+2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 3

15.(曾都区期末)已知x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> mxynx2y2

1)求mn的值;

2)若 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> m <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> n2,求 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 的值.

【分析】(1)将xy直接代入原式即可求出答案.

2)先求出 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 的值,然后根据完全平方公式即可求出答案.

【解答】解:(1)由意得, <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

2)由(1)得, <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

16.(武昌区校级月考)先化简,再求值: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> y2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> x2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 5x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ),其中 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【分析】先把各二次根式化为最简二次根式,再合并得到原式=x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 6 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,接着把xy的值代入,然后进行二次根式的加减运算.

【解答】解:原式=2x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 5 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 6 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> y4时,原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 6 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 6 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

17.(西城区校级月考)先化简,再求值.

6x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> )﹣(4y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ),其中x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> y3

【分析】先把各二次根式化为最简二次根式,然后合并得到原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,最后把xy的值代入计算即可.

【解答】解:原式=6 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 3 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 4 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 6 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> y3时,原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

18.(岳麓区月考)先化简,再求值: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,其中实数ab满足a2+a2b2﹣4ab+b2+10

【分析】根据a2+a2b2﹣4ab+b2+10得出(ab2+ab﹣120,求出ab0ab﹣10,求出ab1,再求出答案即可.

【解答】解:∵a2+a2b2﹣4ab+b2+10

ab2+ab﹣120

ab0ab﹣10

解得:abab1

从已知 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 可知:ab都是正数,

解得:ab1

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

2+1

3

19.(公安县期末)已知 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,若 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,试求a2+b2+ab的值.

【分析】根据题意求出xy的值,然后根据完全平方公式以及平方差公式进行化简,然后将xy代入原式即可求出答案.

【解答】解:由题可知:4﹣x≥0x﹣4≥0

x4

y3

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

原式=(a+b2ab

=( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> )( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

4xxy

4xx+y

3x+y

x4y3时,

原式=12+3

15

20.(江岸区校级月考)化简并求值: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,其中x3y2

【分析】先把各二次根式化为最简二次根式,再合并得到原式=6 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,然后把xy的值代入计算.

【解答】解:原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 5 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

6 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

x3y2,原式=6 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 6 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

21.(上城区校级期末)求值:

1)已知x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,求 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 的值;

2)已知x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,求3x2+4xy+3y2的值.

【分析】(1)先分母有理化得到原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,然后把xy的值代入计算即可;

2)先利用分母有理化得到x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1,再计算出x+y2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> xy1,然后利用完全平方公式得到3x2+4xy+3y23x+y2﹣2xy,最后利用整体代入的方法计算.

【解答】解:(1)原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 时,原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2

2)∵x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1

x+y2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> xy1

3x2+4xy+3y23x+y2﹣2xy2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2﹣2×122

22.(浦东新区校级月考)先化简,再求值:[ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> )•( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ),其中x3y2

【分析】根据二次根式的化简求值即可求解.

【解答】解:原式=( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> •( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

x3y2时,

原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

答:原式的值为 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

23.(宝山区月考)先化简,再求值: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,其中a <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> b3 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【分析】先根据二次根式的混合运算顺序和运算法则化简原式,再将a分母有理化,继而将ab的值代入计算可得.

【解答】解:原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> [ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ]• <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

a <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 3 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> b3 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 时,

原式=2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

2×2

4

24.(饶平县校级期末)先化简,再求值:( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,其中a17﹣12 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> b3+2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【分析】将原式利用二次根式的性质和运算法则化简为 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,由a17﹣12 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 3﹣2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2b3+2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 12,代入计算可得.

【解答】解:原式=( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> )• <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

[ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ]• <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

a17﹣12 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 32﹣2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2=(3﹣2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2

b3+2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2+2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1=( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 12

原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

25.(伊通县期末)先化简,再求值.

6x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> )﹣(4y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ),其中x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1

【分析】将原式进行化简,然后将xy的值代入即可求出答案.

【解答】解:当x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1

原式=(6 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 3 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> )﹣(4 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 6 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

=﹣1

26.(浦东新区期中)化简求值:已知a <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> b <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,求[ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ]• <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> )的值.

【分析】先分母有理化得到a <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1b <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1,再利用因式分解的方法化简[ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ]• <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> )得到2a+2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,然后把a <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1b <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1代入计算即可.

【解答】解:∵a <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1b <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1

[ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ]• <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

[ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ]• <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

=( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ]• <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

2a+2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

a <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1b <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1代入得,原式=2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1+2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2+2

2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 4

27.(海淀区校级月考)已知x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,求 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 的值.

【分析】先将xy的值分母有理化,再代入原式,依据二次根式的混合运算顺序和运算法则计算可得.

【解答】解:当x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 5﹣2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 5+2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 时,

原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

245﹣100 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 98 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 240+245+100 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 98 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 240

970

28.(涪城区校级月考)若xy是实数,且y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,求( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> )﹣( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> )的值.

【分析】先根据二次根式有意义的条件求出x的值,求出y的值,再把根式化成最简二次根式,合并后代入求出即可.

【解答】解:∵xy是实数,且y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

4x﹣1≥01﹣4x≥0

解得:x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> )﹣( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> )的值.

2x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 5 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 3 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 3 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

29.(市中区期中)已知a2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

1)求a2﹣4a+4的值;

2)化简并求值: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【分析】(1)根据完全平方公式把原式变形,把a的值代入计算即可;

2)根据题意得到a1,根据分式的约分法则、二次根式的性质把原式化简,把a的值代入计算即可.

【解答】解:(1)当a2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 时,a2﹣4a+4=(a﹣22=(2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 223

2)∵a2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

a1

原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

a﹣1 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1+2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

3

30.(闵行区期中)先化简,再求值:[ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ] <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,其中x1y2

【分析】先依据二次根式的运算法则化简,再把xy的值代入计算即可.

【解答】解:[ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ] <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

[ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ] <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

x1y2时,原式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/245/" title="训练" class="c1" target="_blank">训练</a> <a href="/tags/282/" title="专题" class="c1" target="_blank">专题</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> .


1