用加减法解下列方程组:3(x+y)-4(x-y)=-18 , 2分之(x+y)+6分之(x-y)=2求解啊,急~
3个回答

3(x+y)-4(x-y)=-18 ①

(x+y)/2+(x-y)/6=2 ②

由②得3(x+y)+(x-y)=12③

③-①得

5(x-y)=30

x-y=6④

④代入③

3(x+y)+6=12

x+y=2⑤

④+⑤

2x=8

x=4

⑤-④

2y=-4

y=-2

方程的解为

{x=4

y=-2

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