1,{2x+y=7 (1) x-y=-4 (2) (1)+(2)得3x=3 解得x=1 将x=1代入(2)得y=5.所以方程得解为x=1 y=5 2.{5(x-y)=x+y,(1) 3x-2y=4.(2) (1)变形得2x-3y=0 (3) (2)*3-(3)*2得5x=12,所以x=12/5,y=8/5.
