Cos3x-cos x/sin x = 0

Question

Cos3x-cos x/sin x = 0

Answer 1

-2sin2xsinx/sinx=0
-2sin2x=0,sinx≠0
2x=πn,n∈z U x≠πk,k∈z
x=πn/2,n∈z U x≠πk,k∈z
x=πn/2,n∈z,n≠2k