Tentukan himpunan dari cos (2x - 20) = -1/2 untuk (0° < x < 360)

cos (2x - 20) = -1/2
cos (2x - 20) = cos 120°

2x - 20 = 120 + k.360
x = 70 + k.180
k = 0, x = 70°
k = 1, x = 250°

2x - 20 = -120 + k.360
x = -50 + k.180
k = 1, x = 130°
k = 2, x = 310°

Hp = {70°;130°;250°;310°}