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