I've uploaded a picture with two problems I'm currently stuck on, I got the first four problems of this type correct, because they were just simple trig functions and whatnot, but now that quotients and complex trig stuff is coming into play I'm getting stuck. For example, on the first one, I don't know what I'd use as u since one term is always contained in another, if that makes sense...

And with the second I just don't understand what to do with that quotient that's there.