Tentukam semua nilai x 2 cos²x +1=3 cos x

2cos² x + 1 = 3 cos x
2 cos² x - 3 cos x + 1 = 0
(2 cos x - 1)(cos x - 1) = 0

2cos x - 1 = 0
cos x = 1/2
x = 60° ± k . 360°

cos x - 1 = 0
cos x = 1
x = k . 360°

Nilai x yg memenuhi :
tergantung interval dr x