3xy²-4x²y-2xy²+5x²y
=xy²+x²y
=xy﹙x+y﹚
∵丨x-1丨+(y+2)²=0
∴x-1=0 x=1
y+2=0 y=-2
∴xy﹙x+y﹚
=-2*1﹙1-2﹚
=2
3xy²-4x²y-2xy²+5x²y=2