1+2cos3xcosx-cos2x=0 Помогите с решением

Question

1+2cos3xcosx-cos2x=0
Помогите с решением

Answer 1

1 + 2cos3xcosx - cos2x = 0
1 + 2·1/2·[cos(3x + x)  + cos(3x - x)] - cos2x = 0
1 + cos4x + cos2x - cos2x = 0
1 + cos4x = 0
cos4x = -1
4x = π + 2πn, n ∈ Z
x =  π/4 + πn/2, n ∈ Z
Ответ: x = π/4 + πn/2, n ∈ Z.