Mikochan Денег не надо,вот :3

sin 3x = 3 sin x - 4 sin^3 x 
sinx+sin3x+cosx=0
4 sin x (1-sin^2 x)+ cos x = 0
(4 sin x cos x + 1) cos x = 0   => cos x = 0  => x = pi/2 + pi m
4 sin x cos x + 1 = 0
2 sin 2x = - 1
sin 2x = -1/2   => 2x = - pi/6 + 2 pi n   => x = - pi/12  + pi n