1+2cos3xcosx-cos2x=0

Помогите с решением

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.