nilai X yang memenuhi persamaan cos (X+2/3 π)- cos(X-2/3π)=1/2√3 untuk 0 ≤ X ≤2π

jawab
2/3 pi = 120

cos(x +120)- cos (x - 120) = 1/2 √3
- 2 sin1/2 (2x) sin 1/2 (240) = 1/2 √3
- 2 sin x  sin 120 = 1/2 √3
- 2 (sin x) (1/2 √3)= 1/2 √3
sin x = - 1/2  = - sin 30
x= 180 + 30 = 210 = 7/6 π
x = 360 - 30 = 330 = 11/6 π