cosx-sin4x=cos3x
cosx - cos3x - sin4x = 0
2sin2x*sinx - 2sinx*cosx = 0
sinx * (sin2x-cosx) = 0
sinx * (2sinx*cos-cosx) = 0
sinx * cosx * (2sinx - 1) = 0
sinx = 0
x = Pik, k прин Z
cosx = 0
x = Pi/2 + Pin, n прин Z
2sinx - 1 = 0
2sinx = 1
sinx = 1/2
x = (-1)^k arcsin 1/2 + Pim, m прин Z
x = (-1)^k Pi/6 + Pim, m прин Z