Question

Verify that this equation is an identity.
Cos(4u)=2cos^2(2u)-1

Answer 1

\[\cos(4u)=2\cos^2(2u)-1\]

Answer 2

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.

Answer 3

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