7X2Y-XY-[3X2Y-2(4XY2-0.5XY)]-4X2Y
=7X2Y-XY-(3X2Y-8XY2+XY)-4X2Y
=7X2Y-XY-3X2Y+8XY2-XY-4X2Y
=8XY2-2XY
=2XY(4Y-1)
=负九分之十
1/2X-2(X-1/3Y2)+(-3/2)X+1/3Y2
=1/2X-2X+2/3Y2-3/2X+1/3Y2
=3X+Y2
=负九分之五十
