Use Inverse Functions Where Needed to Find All Solutions (If $2 \cos ^ { 2 } x - \cos x - 1 = 0$

Multiple Choice

Use inverse functions where needed to find all solutions (if they exist) of the given equation on the interval [0,2π) .​ $2 \cos ^ { 2 } x - \cos x - 1 = 0$ ​

A) ​ $x = \frac { \pi } { 3 } , \frac { 2 \pi } { 3 }$
B) $x = 0 , \frac { 2 \pi } { 3 } , \frac { 4 \pi } { 3 }$
C) $x = 0 , \frac { \pi } { 3 } , \frac { 2 \pi } { 3 }$
D) $x = \frac { \pi } { 3 } , \pi , \frac { 5 \pi } { 3 }$
E) ​solution does not exist