(a-b)^3=(a-b)(a^2-2ab+b^2)=a^3-3a^2b+3ab^2-b^3a^3-b^3=(a-b)(a^2+ab+b^2)
(a-b)^3=a^3-3a^2b+3ab^2-b^3a^3-b^3=(a-b)(a^2+ab+b^2)
