## anonymous 5 years ago Verify that this equation is an identity. Cos(4u)=2cos^2(2u)-1

1. anonymous

$\cos(4u)=2\cos^2(2u)-1$

2. anonymous

Again using the double angle formula.. $cos(4u) = cos^2(2u) - sin^2(2u)$ $sin^2(\theta) + cos^2(\theta) = 1$ Just let $$\theta=2u$$ and solve the bottom for $$sin^2\theta$$ and plug into the top.

3. anonymous

I'm not done but $\sin^2\theta=1-\cos^2\theta$