解
5(a²b-3ab²)-3(a²b-2ab²)
=(5a²b-3a²b)+(-15ab²+6ab²)
=2a²b-9ab²
5xy²-(4xy²-2x²y)+x²y-xy²——这个吗
=(5xy²-4xy²-xy²)+(2x²y+x²y)
=3x²y应该是