Himpunan penyelesaian persamaan cos 2x – 2 cos x = -1, 0≤ x ≤ 2π adallah

Cos 2x – 2cos x = -1
<=> (2cos²x – 1) – 2 cos x + 1 = 0
<=> 2cos²x – 2 cos x = 0
<=> cos²x – cos x = 0
<=> cos x (cos x – 1) = 0
<=> cos x = 0 atau cos x = 1

* cos x = 0
   x = (90, 270)

* cos x = 1
   x = (0, 360)

HP={0, 90, 270, 360}