I'm taught that how to find the general solution for example $\cos 5\theta=\frac{\sqrt{3}}{2}$.

But the exercise given by the book is much more complex than the example. 

For example, $\sin^2 3\theta+\cos 3\theta+1=0$, $\tan \theta=2\csc2\theta$

I've no idea where to start. Can anyone provide me some resource or guide me for this topic? Thanks