Soal Matematika Tingkat SMA

persamaan trigonometri

cos 2x – 2 cos x = -1

2 cos² x – 1 – 2 cos x = -1

cos² x – cos x = 0

cos x (cos x – 1) = 0

cos x = 0 atau cos x = 1

interval 0° ≤ x ≤ 360°

cos x = 0 → x = 90° atau x = 270°

cos x = 1 → x = 0° atau x = 360°

HP = {0° , 90° , 270° , 360°}