错了,是x³y³-1/2x²y+y²-2x³y³+0.5x²y+y²+x³y³-2y²-3
=(x³y³-2x³y³+x³y³)+(-1/2x²y+0.5x²y)+(y²+y²-2y²)-3
=0+0+0-3
=-3
和x,y无关