Prove the identity sin x + 2 sin 3x + sin 5x = 4 cos x sin 3x. Find the general solution (in radians) of

Prove the identity 

sin x + 2 sin 3x + sin 5x = 4 cos² x sin 3x. 

Find the general solution (in radians) of the equation 

sin x + sin 3x + sin 5x = 0.