x³y³-1/2x²y+y²-2x³y³+0.5x²y+y²+x³y³-2y-7
=(x³y³-2x³y³+x³y³)+(-1/2x²y+0.5x²y)+(y²+y²)-2y-7
=0+0+2y²-2y-7
=2y²-2y-7
结果中没有x
所以和x的值无关