.

.
.

.
7x-(5x-5y)-y=7x-5x+5y-y=2x+4y
3x-[5x-(1/2-3)]=3x-[5x+2.5]=-2x-2.5
(2x²-3x+2)-(-5+3x+x²)=2x²-3x+2+5-3x-x²=x²-6x+7
(2y²-4y+1)-(4y²+5y-3)=2y²-4y+1-4y²-5y+3=-2y²-9y+4

题目在那啊？