[tex] \cos^2 \theta= \cos^2 - \sin^2= 2\cos^2\theta-1=1-2\sin^2\theta [/tex] ? The example i was given was [tex] \sin2\theta=2\sin\theta \cos\theta [/tex] this was a little bit easier to understand since there was a left and right side, im not sure how to proove this. How was this formula derived from the sum differnce formula?