Difference of the roots of quadratic formula I have a question to solve with roots quadratic formula that is , 
$$a^3 + b^3 = (a+b)(a^2-ab+b^2)$$
$$(a-b)^3 = a^3 - 3a^2b + 3ab^2 - b^3$$
but I didn't understand how the below formula is generated;
$$\alpha^3 - \beta^3 = (\alpha-\beta)^3+3\alpha\beta(\alpha-\beta)$$

$(\alpha - \beta)^3 +3\alpha\beta(\alpha - \beta) = \alpha^3 -3\alpha^2\beta + 3\alpha\beta^2 -\beta^3+3\alpha^2\beta - 3\alpha\beta^2 =\alpha^3-\beta^3$
