I need help understanding the question: simplify the expression $\displaystyle cos^2(arcsin t)$ using the property that inverses "undo" each other.

I get that $\displaystyle arcsin(t)=sin^-1(t)$ and that that would be the opposite of $\displaystyle sin(t)$. But $\displaystyle cos(t)$ isn't the opposite of $\displaystyle sin(t)$, is it?

Yes, I do know what simplifying is, but I'm not sure how to do it here.