tolong bantuanya kak

2cos² x + cos x - 1 = 0
(2cos x - 1)(cos x + 1) = 0
cos x = 1/2 ---> x = 60° , 300°
cos x = -1 ---> x = 180°

Nilai x yg memenuhi :
60° = 1/3 π
180° = π
300° = 5/3 π