x-y=3-x
2x-y=3
2x-3=y
3(x-y)=5-x 把y=2x-3代入
3(x-2x+3)=5-x
9-3x=5-x
2x=4
x=2 y=2x-3=4-3=1
所以方程组 x=2 y=1
x-41
1-2x/3+1>x
2>5x/3
x