Ал Александра 2cos(x) - 1 = sin(4x) cos(2x) = 2sin(2x)cos(2x) --> cos(2x) = 0 --> sin(2x) = 1/2 --> x = π/4 + πk/2; x = π/12 + πk; x = 5π/12 + πk, k - целое.