# Proving Trig Ident.

by Miike012
Tags: ident, proving, trig
 PF Gold P: 1,153 $$\cos(2s) \equiv \cos^2(s) - \sin^2(s)$$
 PF Gold P: 1,153 Proving Trig Ident. What they did was: $$\frac{2\sin(2s)\cos(2s)}{4} = \frac{2\cdot \left(2\sin(s)\cos(s)\right)\left(\cos^2(s) - \sin^2(s)\right)}{4}$$ which is simply substituting in $$2\sin(s)\cos(s)$$ for $$\sin(2s)$$, and $$\cos^2(s)-\sin^2(s)$$ for $$\cos(2s)$$.