{x-y=-3.7x+5y=0.

问题描述:

{x-y=-3.7x+5y=0.

x-y=-3 → x=y-3.代入7x+5y=0.得 7﹙y-3﹚+5y=0
y=7/4
x=y-3=7/4-3=-5/4