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【323850】2024八年级数学下册 第1章二次根式(典型30题专练)(含解析)(新版)浙教版

时间:2025-01-15 20:49:25 作者: 字数:17409字
简介:


 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1章二次根式(典型30题专练)

一.选择题(共7小题)

1.(海伦市期末)若二次根式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 在实数范围内有意义,则a的取值范围是(  )

Aa2 Ba≤2 Ca≠2 Da≥2

【分析】二次根式的被开方数是非负数.

【解答】解:依题意,得

a﹣2≥0

解得,a≥2

故选:D

【点评】考查了二次根式的意义和性质.概念:式子 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> a≥0)叫二次根式.性质:二次根式中的被开方数必须是非负数,否则二次根式无意义.

2.(江北区校级期末)下列各式中,是最简二次根式的是(  )

A <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> C <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> D <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【分析】最简二次根式的概念:被开方数不含分母;被开方数中不含能开得尽方的因数或因式.根据最简二次根式的概念判断即可.

【解答】解:A选项,被开方数中含有分母,不是最简二次根式,不符合题意;

B选项, <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2,被开方数中含有能开得尽方的因数,不符合题意;

C选项, <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,被开方数中含有能开得尽方的因数,不符合题意;

D选项, <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 是最简二次根式,符合题意.

故选:D

【点评】本题考查了最简二次根式的概念,熟练掌握二次根式的概念是解题的关键.

3.(永嘉县校级期中)下列式子成立的是(  )

A <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ±9 B <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> C <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> D <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【分析】直接根据二次根式的性质化简判断即可.

【解答】解: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 9,故选项A错误;

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2,故选项B错误;

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2,故选项C错误;

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> =﹣1,故选项D正确.

故选:D

【点评】此题考查的是二次根式的性质,掌握其性质是解决此题关键.

4.(峨眉山市模拟)若代数式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 有意义,则x的取值范围是(  )

Ax≥2 Bx≥0 Cx≥0x≠2 Dx≠2

【分析】根据二次根式的性质和分式的意义,被开方数大于等于0,分母不等于0,就可以求解.

【解答】解:根据二次根式有意义得:x≥0

分式有意义,得x﹣2≠0,解得x≠2

综上所述,x的取值范围是x≥0x≠2

故选:C

【点评】本题考查了二次根式的性质和分式的意义.涉及的知识点为:分式有意义,分母不为0;二次根式的被开方数是非负数.

5.(宁阳县期末)要使二次根式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 有意义,那么x的取值范围是(  )

Ax≥1 Bx1 Cx1 Dx≥﹣1

【分析】根据二次根式有意义的条件列出不等式,解不等式得到答案.

【解答】解:由题意得,2x﹣2≥0

解得,x≥1

故选:A

【点评】本题考查的是二次根式有意义的条件,掌握二次根式的被开方数是非负数是解题的关键.

6.(望城区期末)在 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 中,与 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 是同类二次根式的有几个(  )

A1 B2 C3 D4

【分析】先根据二次根式的性质化成最简二次根式,再根据同类二次根式的定义判断即可.

【解答】解:∵ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 是同类二次根式的有 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,共2个,

故选:B

【点评】本考查了同类二次根式的定义,注意:几个二次根式化成最简二次根式后,如果被开方数相同,那么这几个二次根式叫同类二次根式.

7.(硚口区月考)下列各式中正确的是(  )

A <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> =﹣5 B <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ±4 C.(﹣ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 29 D <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【分析】直接利用二次根式的性质与化简、二次根式乘法运算法则分别判断得出答案.

【解答】解:A. <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 5,故此选项错误;

B. <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 4,故此选项错误;

C.(﹣ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 23,故此选项错误;

D. <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,故此选项正确.

故选:D

【点评】此题主要考查了二次根式的性质与化简、二次根式乘法运算,正确掌握二次根式乘法运算法则是解题关键.

二.填空题(共12小题)

8.(铁西区期末)若最简二次根式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 能合并成一项,则a ﹣1 

【分析】由题意可知该二次根式为同类二次根式.

【解答】解:由题意可知: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

a+32

a=﹣1

故答案为:﹣1

【点评】本题考查二次根式,解题的关键是正确运用同类二次根式的概念,本题属于基础题型.

9.(永嘉县校级期中)( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2 7  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  

【分析】根据二次根式的运算法则即可求出答案.

【解答】解:( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 27

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

故答案为:735 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【点评】本题考查二次根式,解题的关键是熟练运用二次根式的运算法则,本题属于基础题型.

10.(大庆) <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  2 

【分析】直接利用二次根式的性质化简得出答案.

【解答】解: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2

故答案为:2

【点评】此题主要考查了二次根式的性质与化简,正确化简二次根式是解题关键.

11.(德城区一模)在式子 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 中,x的取值范围是 x>﹣1 

【分析】根据二次根式有意义的条件、分式有意义的条件列出不等式,解不等式得到答案.

【解答】解:由题意得,x+10

解得,x>﹣1

故答案为:x>﹣1

【点评】本题考查的是二次根式有意义的条件、分式有意义的条件,掌握二次根式的被开方数是非负数、分式的分母不为0是解题的关键.

12.(郫都区期末)分母有理化: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  

【分析】给分子分母同乘以(2﹣ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ),分母即可化为平方差形式去掉根式,再进行计算即可得出答案.

【解答】解: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

故答案为:2﹣ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【点评】本题主要考查了分母有理化及二次根式的乘除,合理运用分母有理化法则进行计算是解决本题的关键.

13.(新蔡县期末)若二次根式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 是最简二次根式,则x可取的最小整数是 ﹣2 

【分析】根据最简二次根式的定义解答即可.

【解答】解:∵二次根式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 是最简二次根式,

2x+7≥0

2x≥﹣7

x≥﹣3.5

x取整数值,

x=﹣3时,二次根式为 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1,不是最简二次根式,不合题意;

x=﹣2时,二次根式为 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,是最简二次根式,符合题意;

若二次根式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 是最简二次根式,则x可取的最小整数是﹣2

故答案为:﹣2

【点评】本题主要考查了最简二次根式的定义,熟记定义是解答此题的关键.

14.(饶平县校级期末)已知 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 是整数,自然数n的最小值为 2 

【分析】根据自然数和二次根式的性质得出18﹣n16,求出即可.

【解答】解:∵ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 是整数,n为最小自然数,

18﹣n16

n2

故答案为:2

【点评】本题考查了二次根式的定义,能根据题意得出18﹣n16是解此题的关键.

15.(衡阳)若二次根式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 有意义,则x的取值范围是 x≥3 

【分析】二次根式的被开方数x﹣3≥0

【解答】解:根据题意,得

x﹣3≥0

解得,x≥3

故答案为:x≥3

【点评】考查了二次根式的意义和性质.概念:式子 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> a≥0)叫二次根式.性质:二次根式中的被开方数必须是非负数,否则二次根式无意义.

16.(连云港)计算: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  5 

【分析】根据二次根式的基本性质进行解答即可.

【解答】解:原式= <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 5

故答案为:5

【点评】本题考查的是二次根式的性质与化简,熟知二次根式的基本性质是解答此题的关键.

17.(永嘉县校级期中)已知y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ﹣5,则(x+y2021 ﹣1 

【分析】依据二次根式有意义的条件,即可得到xy的的值,进而得出(x+y2021的值.

【解答】解:∵y <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ﹣5

x﹣4≥04﹣x≥0

解得x4

y=﹣5

x+y2021=(﹣12021=﹣1

故答案为:﹣1

【点评】本题主要考查了二次根式有意义的条件,如果一个式子中含有多个二次根式,那么它们有意义的条件是:各个二次根式中的被开方数都必须是非负数.

18.(余杭区模拟)已知x2+ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,则代数式(7﹣4 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> x2+2﹣ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 的值为 2﹣ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  

【分析】将x2+ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 代入代数式(7﹣4 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> x2+2﹣ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,先利用完全平方公式和平方差公式化简计算,再进行实数的混合运算即可得出答案.

【解答】解:∵x2+ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> x2+2﹣ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> +4﹣3)﹣ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

49﹣48+1﹣ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

故答案为:2﹣ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【点评】本题考查了二次根式的化简求值,熟练掌握完全平方公式和平方差公式及二次根式的混合运算法则是解题的关键.

19.(永嘉县校级期中)当x=﹣1时,二次根式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 的值是 3 

【分析】把x=﹣1代入二次根式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,再开平方即可.

【解答】解:把x=﹣1代入 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 3

故答案为:3

【点评】此题主要考查了二次根式定义,关键是掌握算术平方根.

三.解答题(共11小题)

20.(永嘉县校级期中)计算:

1 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【分析】(1)利用二次根式的性质计算;

2)利用二次根式的乘除法则运算.

【解答】解:(1)原式=3﹣8+3

=﹣2

2)原式= <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【点评】本题考查了二次根式的混合运算:先把二次根式化为最简二次根式,然后合并同类二次根式即可.在二次根式的混合运算中,如能结合题目特点,灵活运用二次根式的性质,选择恰当的解题途径,往往能事半功倍.

21.(淮北月考)如果最简二次根式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 是同类二次根式.

1)求出a的值;

2)若ax≤2a,化简: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【分析】(1)利用同类二次根式的定义求出a的值即可;

2)把a的值代入确定出x的范围,原式变形后,利用二次根式性质化简,即可求出值.

【解答】解:(1)∵最简二次根式 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 是同类二次根式,

4a﹣513﹣2a

解得:a3

2)把a3代入得:3≤x≤6

则原式= <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> |x﹣2|+|x﹣6|x﹣2+6﹣x4

【点评】此题考查了同类二次根式,最简二次根式,熟练掌握各自的性质是解本题的关键.

22.(永嘉县校级模拟)计算:| <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【分析】先进行二次根式的乘法运算,然后把二次根式化为最简二次根式后合并即可.

【解答】解:原式=2﹣ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【点评】本题考查了二次根式的混合运算:先把二次根式化为最简二次根式,然后合并同类二次根式即可.在二次根式的混合运算中,如能结合题目特点,灵活运用二次根式的性质,选择恰当的解题途径,往往能事半功倍.

23.(古丈县期末)已知x2﹣ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,求下列代数式的值:

1x2+2xy+y2;(2x2y2

【分析】(1)根据已知条件先计算出x+y4,再利用完全平方公式得到x2+2xy+y2=(x+y2,然后利用整体代入的方法计算;

2)根据已知条件先计算出x+y4xy=﹣2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,再利用平方差公式得到x2y2=(x+y)(xy),然后利用整体代入的方法计算.

【解答】解:(1)∵x2﹣ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

x+y4

x2+2xy+y2=(x+y24216

2))∵x2﹣ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

x+y4xy=﹣2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

x2y2=(x+y)(xy

(﹣2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

=﹣8 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【点评】本题考查了二次根式的化简求值:先根据二次根式的性质和运算法则进行化简,然后把满足条件的字母的值代入求值.

24.(永嘉县校级期末)计算:

1 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2+π+ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 0

2)( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【分析】(1)直接利用负整数指数幂的性质以及零指数幂的性质和二次根式的性质分别化简得出答案;

2)直接利用二次根式的混合运算法则计算得出答案.

【解答】解:(1)原式=2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ﹣1+9+1

2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> +1+9+1

11

2)原式= <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【点评】此题主要考查了零指数幂的性质以及二次根式的混合运算等知识,正确掌握相关运算法则是解题关键.

25.(海淀区校级期中)已知x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1,求代数式x2+2x﹣6的值.

【分析】直接将原式分解因式,再把x的值代入进而计算得出答案.

【解答】解:x2+2x﹣6=(x+12﹣7

x <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

5﹣7

=﹣2

【点评】此题主要考查了二次根式的化简求值,正确运用乘法公式是解题关键.

26.(黄冈月考)如图,实数ab在数轴上的位置,化简 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【分析】根据数轴表示数的方法得到a0b,再根据二次根式的性质得原式=|a|﹣|b|﹣|ab|,然后去绝对值后合并即可.

【解答】解:∵a0b

原式=|a|﹣|b|﹣|ab|

=﹣ab+ab

=﹣2b

【点评】本题考查了二次根式的性质与化简: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> |a|.也考查了实数与数轴.

27.(饶平县校级期末)观察下列等式:回答问题:

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,…

1)根据上面三个等式的信息,猜想 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  

2)请按照上式反应的规律,试写出用n表示的等式;

3)验证你的结果.

【分析】根据观察,可得规律: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【解答】解:(1)根据上面三个等式的信息,猜想 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

故答案为:1 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【点评】本题考查了算术平方根,观察等式发现规律是解题关键.

28.(寻乌县期末)在进行二次根式化简时,我们有时会碰上如 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 一样的式子,其实我们还可以将其进一步化简: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

以上这种化简的步骤叫做分母有理化. <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 还可以用以下方法化简: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

1)请用不同的方法化简 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

2)化简: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【分析】(1)分式的分子和分母都乘以 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,即可求出答案;把2看出5﹣3,根据平方差公式分解因式,最后进进约分即可.

2)先每一个二次根式分母有理化,再分母不变,分子相加,最后合并即可.

【解答】解:(1 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

2)原式= <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【点评】本题考查了分母有理化,平方差公式的应用,主要考查学生的计算和化简能力.

29.(永嘉县校级期末)【知识链接】

1)有理化因式:两个含有根式的非零代数式相乘,如果它们的积不含有根式,那么这两个代数式相互叫做有理化因式.

例如: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 的有理化因式是 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 的有理化因式是1+ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

2)分母有理化:分母有理化又称“有理化分母”,也就是把分母中的根号化去.指的是如果代数式中分母有根号,那么通常将分子、分母同乘分母的有理化因式,达到化去分母中根号的目的.如:

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【知识理解】

1)填空:2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 的有理化因式是  <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  

2)直接写出下列各式分母有理化的结果:

 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>  

【启发运用】

3)计算: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【分析】12 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2x即可找出2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 的有理化因式

2分式中分子、分母同时× <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ),即可得出结论;分式中分子、分母同时×3 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ),即可得出结论;

3)利用分母有理化将原式变形为 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,合并同类项即可得出结论.

【解答】解:(1)∵2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2x

2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 的有理化因式是 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

故答案为: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

故答案为: <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

3)原式= <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1

【点评】本题考查了分母有理化,解题的关键是:(1)由2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2x,找出2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 的有理化因式;(2)根据平方差公式,将各式分母有理化;(3)利用分母有理化将原式变形为 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

30.(永嘉县校级期末)阅读下面的解答过程,然后作答:

有这样一类题目:将 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 化简,若你能找到两个数mn,使m2+n2amn <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> ,则a+2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 可变为m2+n2+2mn,即变成(m+n2,从而使得 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> m+n,化简:

例如:∵5+2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 3+2+2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

请你仿照上例将下列各式化简:

1 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【分析】(1)利用完全平方公式把4+2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 化为(1+ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2,然后利用二次根式的性质化简即可.

2)利用完全平方公式把7﹣2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 化为( <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 2然后利用二次根式的性质化简即可.

【解答】解:(1)∵4+2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 1+3+2 <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a> 12+ <a href="/tags/55/" title="数学" class="c1" target="_blank">数学</a> <a href="/tags/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</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/96/" title="典型" class="c1" target="_blank">典型</a> <a href="/tags/896/" title="根式" class="c1" target="_blank">根式</a>

【点评】本题主要考查了二次根式的性质与化简,解题的关键是熟记掌握完全平方公式.


1