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【329728】5.2 求解二元一次方程组 同步练习3

时间:2025-02-03 19:06:14 作者: 字数:2346字


 <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a>

求解二元一次方程组

一、认真选择

1)用代入法解方程组 <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a> 的最佳策略是( )

A.y,由②得y= <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a> (239x) B.x,由①得x= <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a> (5y+2)

C.x,由②得x= <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a> (232y) D.y,由①得y= <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a> (3x2)

2)解以下两个方程组,较为简便的是( )

 <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a> <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a>

A.①②均用代入法 B.①②均用加减法

C.①用代入法②用加减法 D.①用加减法②用代入法

3)若方程组 <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a> 的解互为相反数,则m的值等于( )

A.7 B.10 C.10 D.12

4)不解方程组,下列与 <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a> 的解相同的方程组是( )

A. <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a> B. <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a> C. <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a> D. <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a>

二、看谁做得又对又快

1)若-3xa2by72x8y5a+b是同类项,则a=__________,b=__________.

2)已知(3x2y+1)2|4x3y3|互为相反数,则x=_______,y=__________.

3)已知y=kx+b,x=1时,y=1,当x=3时,y=5,k=____,b=_______.

三、解下列方程组

1 <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a>



2 <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a>



四、解答题

小明和小华同时解方程组 <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a> ,小明看错了m,解得 <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a> ,小华看错了n,解得 <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a> ,你能知道原方程组正确的解吗?



灵机一动:

小明的外婆送来满满一篮鸡蛋,这只篮子最多只能装55只左右的鸡蛋.小明3只一数,结果剩下1只,但忘了数多少次,只好重数,他5只一数剩2只,可又忘了数多少次.他准备再数时,妈妈笑着说:“不用数了,共有52.”小明很惊讶,妈妈笑而未答,让他好好动脑筋想想.后来,他用方程知识解决了这个问题,你知道小明是怎样解决的吗?

测验评价结果:________;对自己想说的一句话是:__________________



参考答案

一、(1)B (2)C (3)C (4)A

二、(1)2 3 (2)9 13 (3)2 1

三、(1) <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a> (2) <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a>

四、根据题意得: <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a> 是方程2xny=13的解 <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a> 是方程mx+y=5的解

所以有:2× <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a> +2n=13,3m7=5

n=3,m=4

原方程组即为 <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a>

解得 <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a> 即为正确的解.

灵机一动:

设这只篮子装了m只鸡蛋,每3只一数,数了x次剩1,每5只一数,数了y次剩2,则有 <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a> ,消去m得,3x+1=5y+2,即y= <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a>

xy都是正整数,3x+155左右的数

3x1必是53左右的数,且能被5整除

3x1=55时,x=18 <a href="/tags/48/" title="练习" class="c1" target="_blank">练习</a> <a href="/tags/50/" title="同步" class="c1" target="_blank">同步</a> <a href="/tags/380/" title="方程" class="c1" target="_blank">方程</a> ,不合题意

3x1=50时,x=17,m=3x+1=52符合题意

这一篮鸡蛋共有52