sin (x-π/3)+sin(x-4π/3)=

Rumus Jumlah dan Perkalian

sin A  + sin B = 2 sin 1/2 (A+B) cos 1/2 (A-B)

sin(x - π/3) + sin (x -  4π/3)
A = x - π/3
B = x- 4π/3
A+B = 2x - 5π/3
A-B = π

sin (x - π/3)  + sin (x -  4/3 π) =
= 2 sin 1/2 (2x  - 5π/3) . cos (π)
= 2 sin (x - 5π/6).(-1)
= -2 sin (x -  5π/6)