解方程组：2(x+y)-3(x-y)=3；4(x+y)+3x=15+3y.

显示全部楼层 · 2013-4-1 13:36:49

2(x+y)-3(x-y)=32x+2y-3x+3y=3-x+5y=3............-7x+35y=21.........(1)4(x+y)+3x=15+3y4x+4y+3x=15+3y7x+y=15.........(2)(1)+(2)得到：36y=36y=1y=1带入-x+5y=3x=2...

千问 · 2013-4-1 13:36:49

解：2（x+y)-3(x-y)=3；4（x+y) +3x=15+3y2x+2y-3x+3y=3;4x+4y+3x=15+3y-x+5y=3;7x-y=156x+4y=186x=18-4yx=18-4y /6x=3-2/3y把x=3-2/3y代入7x-y=15得7(3-2/3y)-y=15解得:y=18/11把y=18/11代入x=3-2/...

千问 · 2013-4-1 13:36:49

2(x+y)-3(x-y)=3
2x+2y-3x+3y-3=0
x-5y+3=0
8x-40y+24=0（1）4(x+y)+3x=15+3y
4x+4y+3y-15-3y=8x-15=0（2）
（1）减（2）=-40y+39=0 解得y=39/40...