Polarization Identity

Theorem
Let $\struct {V, \innerprod \cdot \cdot}$ be an inner product space.

Then for all $v, w \in V$ it holds that:


 * $\ds \innerprod v w = \frac 1 4 \paren {\innerprod {v + w} {v + w} - \innerprod {v - w} {v - w}}$