3x³-5x²y+xy²+y³=3x³-3x²y-2x²y+2xy²-xy²+y³=3x²(x-y)-2xy(x-y)-y²(x-y)=(x-y)(3x²-2xy-y²)=(x-y)(x-y)(3x+y)=(x-y)²(3x+y)