Trigonometric double angle formulas problem I want to simplify the answer to an equation I had to compute, namely, simplifying $\sin^2 (2y) + \cos^2 (2y)$. I know that $\sin^2 (y) + \cos^2 (y) = 1$ but is there anything like that I can use at all?

I strongly hope that you know, sine and cosine are functions and aren't being multiplied by angles.
$$\cos^2{x}+\sin^2{x}=1$$
where, $x \in \mathbb R$ and so therefore, $2x \in \mathbb R$
For instance:
$$\cos^2{30^o}+\sin^2{30^o}=\cos^2{60^o}+\sin^2{60^o}$$
$$1=1$$
