Hello all. I am having trouble with a trig identity, and was wondering if you could help. This is a problem from a take home quiz, and unfortunately I can't find anything in my text about how to deal with the $\displaystyle \cos{4\theta}$.

Here is the identity.

$\displaystyle \sin^2\theta\cos^2\theta=\frac{1}{8}[1-\cos{4\theta}]$