Mohon bantuannya dan uraiannyaa

sin 3x + sin x = 2 cos x
2 sin (3x + x)/2 cos (3x - x)/2 = 2 cos x
2 sin 2x cos x - 2 cos x = 0
2 cos x (sin 2x - 1) = 0

1) 2 cos x = 0
cos x = 0
cos x = cos 90°
x = 90° = π/2

2) sin 2x - 1 = 0
sin 2x = 1
sin 2x = sin 90°
2x = 90°
x = 45° = π/4