himpunan penyelesaian

cos a + cos b = 2 cos ((a+b):2) cos ((a+b):2)
cos ( x+60) + cos (x-60) = 1/2 √3
2 cos (x) cos (60) = 1/2 √3
2 cos (x) 1/2 = 1/2 √3
cos x = 1/2 √3 = cos 30

(i). x = 30 + k.360
k = 0 maka x = 30

(ii). x = -30 + k.360
k = 1 maka k = 330

hp = {30,330}