(a+2b)*(a^2-2ab+4b^2) = a\^3+2ab^2-a^2b-2ab^2+4b^3= a\^3-a^2b+2b^3
(a-b+c)*(a+b-c) = a^2+ab-ac-ab-b^2+bc = a^2 - b^2 + bc - ac
(a+2b)(a-2b)(a^2+4b^2) = (a^2-4b^2)*(a^2+4b^2) = a^4 - 16b^4
(a+2b)*(a^2-2ab+4b^2) = a\^3+2ab^2-a^2b-2ab^2+4b^3= a\^3-a^2b+2b^3
(a-b+c)*(a+b-c) = a^2+ab-ac-ab-b^2+bc = a^2 - b^2 + bc - ac
(a+2b)(a-2b)(a^2+4b^2) = (a^2-4b^2)*(a^2+4b^2) = a^4 - 16b^4