$\begin{array}{1 1}(A)\;x=n\pi+(-1)^n\large\frac{7\pi}{6}&(B)\;x=2n\pi+(-1)^n\large\frac{\pi}{6}\\(C)\;x=3n\pi+(-1)^n\large\frac{\pi}{6}&(D)\;x=4n\pi+(-1)^n\large\frac{\pi}{6}\end{array} $
