2x^2y+4xy^2=2xy(x+2y)
100a-a^3=a(100-a^2)=a(10-a)(10+a)
ab+ac-4b-4 c =a(b+c)- 4(b+c)=(b+c)(a-4)
2x^2y+4xy^2=2xy*(2y+x)
100a-a^3=(10-a)*a*(a+10)
ab+ac-4b-4c=(a-4)*(c+b)
