(1+cos4x)*sin2x=cos^2(2x)
1+ cos4x = cos²2x + sin²2x + cos²2x - sin²2x = 2 cos²2x
Имеем: 2 cos²2x * sin2x = cos²2x
sin2x = cos²2x / 2cos²2x
sin2x = 1/2
2x = (-1)^n arcsin 1/2 + pi n, n e Z
2x = (-1)^n pi/6 + pi n, n e Z
x = (-1)^n pi/12 + (pi n)/2, n e Z