解几个方程

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2 | 2009-6-8 14:09:38 | 显示全部楼层 |阅读模式

1.设2x+3y=a,2x-3y=b,根据换元法得方程组:a/4+b/3=7a/3+b/2=8整理得:3a+4b=84
(1)2a+3b=48
(2)(1)*2,(2)*3得:6a+8b=168 (3)6a+9b=144 (4)(3)-(4)得:-b=24 b=-24解方程组得:a=60b=-24即得到方程组:2x+3y=602x-3y=-24两式相加得:4x=36 x=9解方程组得:x=9y=142.(x-3)÷0.5-(x+4)÷0.2<=4(x-3)÷(1/2)-(x+4)÷(1/5)<=42...

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