mohon bantu jawab yaa no 18. trims

18. trigonometri

sin 3x  + sin x = 2 cos x , pada  0≤ x ≤ π/2
2 sin 1/2 (3x+x) cos 1/2 (3x-x) = 2 cos x
2 sin 2x cos x = 2 cos x  ....bagi dengan 2 cos x
sin 2x = 1 = sin π/2
2x = π/2 + k. 2π  
x = π/4 + k. π , k = 0,1,2,3,..
k = 0 , x = π/4
k = 1 , x  = 5π/4  (tm)

x = (π/4)