4 cos³x = sin(х-3π/2) 4 cos³x = -sin(3π/2 - х) 4 cos³x = сosх cos²x = 1/4 1) cosx = 1/2 х₁ = ±π/3 + 2πn n∈Z 2) cosx = -1/2 х₂ = ±2π/3 + 2πn n∈Z
