The number of possible solutions of $$\sin \theta+\sin 4 \theta+\sin 7 \theta=0, \theta \in(0, \pi)$$ are

The number of solutions of $$\tan x+\sec x=2 \cos x$$ in $$[0,2 \pi]$$ are

The number of solutions in $$[0,2 \pi]$$ of the equation $$16^{\sin ^2 x}+16^{\cos ^2 x}=10$$ is

The principal solutions of $$\cot x=\sqrt{3}$$ are