-7x³y-14x²y² =-7x²y(x+2y)
3x³+9x² =3x²(x+3)
x²-3x =x(x-3)
2x²-4xy=2x(x-2y)
5a-20 =5(a-4)
a³+2a²b=a²(a+2b)
m²-m=m(m-1)
6+2a=2(3+a)
3m²-12=3(m²-4)=3(m+2)(m-2)6(m-n)³-3(n-m)²6(m-n)³-3(n-m)²=6（m-n)³-3(m-n)²=3(m-n)²[2(m-n)-1]=3(m-n)(2m-2n-1)