1、x³-2x²y+xy²；
=x(x²-2xy+y²)
=x(x-y)²
2、（x+y）²-3（x+y）；
=(x+y){(x+y)-3]
=(x+y)(x+y-3)
3、x²+8x+16
=(x+4)²
4、2x²-12x+18；
=2(x²-6x+9)
=2(x-3)²
5、9a-a³
=-a(a²-9)
=-a(a+3)(a-3)