Find the general solution for the equation $\cos 3x+\cos x-\cos 2x=0$

Question

$\begin{array}{1 1}(A)\;x=2n\pi\pm \large\frac{\pi}{3}&(B)\;x=n\pi\pm \large\frac{\pi}{3}\\(C)\;x=2n\pi\pm \large\frac{\pi}{4}&(D)\;x=2n\pi\pm \large\frac{\pi}{6}\end{array} $