## gjhfdfg Group Title Use an angle sum identity to verify the identity cos 2 (theta) = 2 cos^2 (theta) - 1 2 years ago 2 years ago

1. zepdrix

Rewrite it like this. $\cos(2\theta)=\cos(\theta + \theta)$ Then you need to remember your angle sum identity for cosine :) $\cos(\alpha+\beta) = \cos \alpha \cos \beta - \sin \alpha \sin \beta$ See if you can figure it out from there! :)

2. gjhfdfg

So, 2+2? for a + b?

3. zepdrix

Theta + Theta for a and b :\