The second one is an example our instructor gave us, but I can't figure out where she got the "0" for cos and sin -

With this problem, we try to find the derivative of the inverse of f(x) where g(x) is the inverse:

Now here's the part where she skipped a lot of stuff

(SiMoon says : I don't think she did, you'll see below ) and literally put this on the board:

Where did she get "0" from? I have no idea where that fits into the problem.

Any help I can get would be awesome, even if it's just a hint.

Thanks!