4 cos^3x = sin(х-3π/2) 4 cos^3x = -sin(3π/2 - х) 4 cos^3x = сosх cos^2x = 1/4 1) cosx = 1/2 2) cosx = -1/2 х1 = ±π/3 + 2πn n∈Z х2= ±2π/3 + 2πn n∈Z