Well, since I only get an error message telling me that my latex syntax is wrong, I've used this LaTeX engine and pasted the images to this forum.

This is the equation I'm having problems with:

I have rewritten this in terms of sine, like this:

So the equation now looks like this:

I have tried all sorts of things to find the right answer, but I am unable to. This is one of the things I've tried:

But I can't get to the correct answers from this value. Ofcourse I've added +2k pi etc, but I must be doing something wrong. Please help me