The general solution of $$2 \cos 4 x+\sin ^2 2 x=0$$ is

Find the general solution of $$\sin 2x + \cos x = 0$$.

If $$\sin 2x = 4\cos x$$, then x is equal to

If $$\sin 3\theta = \sin \theta $$, how many solutions exist such that $$ - 2\pi < \theta < 2\pi $$?