Hp dari 2cos² 5x - 5cos5x - 3 = 0

2.cos²5x - 5.cos 5x - 3 = 0
(2cos 5x + 1)(cos 5x - 3) = 0
2cos 5x + 1 = 0
2cos 5x = -1
cos 5x = -½
cos 5x = cos 120°
5x = 120
x = 120/5
x = 24°
cos 5x = cos 240°
5x = 240
x = 240/5
x = 48°
cos 5x - 3 = 0
cos 5x = 3 (tidak memenuhi)
hp {24°, 48°}