If $$0 \le x < 2\pi $$, then the number of real values of $$x$$, which satisfy the equation $$\,\cos x + \cos 2x + \cos 3x + \cos 4x = 0$$ is:

The number of values of $$x$$ in the interval $$\left[ {0,3\pi } \right]\,$$ satisfying the equation $$2{\sin ^2}x + 5\sin x - 3 = 0$$ is

The number of solution of $$\tan \,x + \sec \,x = 2\cos \,x$$ in $$\left[ {0,\,2\,\pi } \right]$$ is