Cosxcos3x - sin3xsinx = 1/2
Cosxcos3x - sin3xsinx = 1/2 cos(3x + x) = 1/2 cos 4x = 1/2 4x = ±п/3 + 2пn , n ∈ Z |:4 x = ±п/12 + пn/2, n ∈ Z