Sum of Two Odd Powers/Examples/Sum of Two Cubes/Proof 1

Proof
From Difference of Two Powers:
 * $\ds a^n - b^n = \paren {a - b} \sum_{j \mathop = 0}^{n - 1} a^{n - j - 1} b^j$

Let $x = a$ and $y = -b$.

Then: