Question

Precalc:
Verify the identity.
cos 4x + cos 2x = 2 - 2 sin2 2x - 2 sin2 x

Answer 1

Is this your equation?\[\cos4x+\cos2x=2-2\sin^22x-2\sin^2x\]

Answer 2

@SithsAndGiggles yes

Answer 3

Okay. I think working with the left side would be easier. Use the following identity:
\[\cos2x=\cos^2x-\sin^2x\]
Note that the above identity also gives you
\[\cos2x=1-2\sin^2x=2\cos^2x-1\]
\[\cos4x+\cos2x=\cdots\\
(\cos^22x-\sin^22x)+(\cos^2x-\sin^2x)=\cdots\\
(1-2\sin^22x)+(1-2\sin^2x)=\cdots\]

Answer 4

@SithsAndGiggles thanx :)

Answer 5

You're welcome