I'll try to help by way of an example. Consider . To find the derivative of this it's best to take sines of both sides to get to a derivative you already know, specifically:

From here, the derivative with respect to (not !) is:

which becomes

Hopefully these steps are fairly clear? We know from the start of the question that , so

but this is a pretty ugly answer. It can be improved by considering the trig identity:

but we know , so

and therefore

I hope that helps!