Find All Solutions of the Given Equation in the Interval $\pi$

Multiple Choice

Find all solutions of the given equation in the interval [0, 2 $\pi$ ) .
$\cos 3 x = \cos x$

A) $x = 0 , \frac { \pi } { 2 } , \pi , \frac { 3 \pi } { 2 }$
B) $x = \frac { \pi } { 4 } , \frac { \pi } { 2 } , \frac { 3 \pi } { 2 }$
C) $x = 0 , \frac { \pi } { 4 } , \frac { \pi } { 2 } , \pi$
D) $x = 0 , \frac { \pi } { 4 } , \pi , \frac { 3 \pi } { 4 }$
E) $x = \frac { \pi } { 8 } , \frac { 2 \pi } { 8 } , \frac { \pi } { 2 } , \frac { 3 \pi } { 8 } , \pi , \frac { 3 \pi } { 2 }$