1.x³-x²y-xy²+y³ 2.y²-2y-15 3.已知a+b=

1.x³-x²y-xy²+y³
=x(x²-y²)-y(x²-y²)
=(x²-y²)(x-y)
=(x-y)²(x+y)
2.y²-2y-15
=(y-5)(y+3)
3.已知a+b=2,ab=2,求
1/2a³b+a²b²+1/2ab³
=1/2ab(a²+2ab+b²)
=1/2ab(a+b)²
=1/2×2×2²
=4