# Math Help - trig help...

1. ## trig help...

cos(alpha - beta) cos(alpha + beta) = cos squared alpha - sin squared beta

2. Originally Posted by Valaina
cos(alpha - beta) cos(alpha + beta) = cos squared alpha - sin squared beta
use the sum/difference identity for cosine ...

$\cos(a \pm b) = \cos(a)\cos(b) \mp \sin(a)\sin(b)$

btw ... this should have been posted in the trig section.