sin 2x - sin x = 2cos x - 1
2sin x cos x - sin x = 2cos x - 1
sin x (2cos x - 1) - (2cos x -1) = 0
(2cos x - 1)(sin x - 1) = 0
2cos x - 1 = 0; x = ±π/3 + 2πn,n ∈ Z
sin x - 1 = 0; x = π/2 + 2πk,k ∈ Z
