(a-3)^2+(3-a)
=(a-3)^2-(a-3)
=(a-3)[(a-3)-1]
=(a-3)(a-4)
5(x-y)^3+10(y-x)^2
=5(x-y)^3+10(x-y)^2
=5(x-y)^2[(x-y)+2]
=5(x-y)^2(x-y+2)