# Math Help - need to prove this cross product

1. ## need to prove this cross product

to to show that (a - b) x (a + b) = 2(a x b)

$u \times \left( {a + b} \right) = \left( {u \times a} \right) + \left( {u \times b} \right)$.
Let $u=a-b$ and apply again.