yaitu
π/3, 4π/3, π
Pembahasan:
cos2x + cosx = 0
2cos²x – 1 + cosx = 0
2cos²x + cosx – 1 = 0
(2cosx – 1)(cosx +1) = 0
⇒ 2cosx – 1 = 0
cosx = ½
x = π , 4π
3 3
⇒ cos x + 1 = 0
cosx = –1
x = π
Jadi, Hp : π , 4π, π
3 3