Cos(3x) = 2Sin(3π/2 + x) Cos(3x) = -2Cosx Cos(3x) + 2Cosx = 0 4Cos³x - 3Cosx + 2Cosx = 0 4Cos³x - Cosx = 0 1) Замена: Cosx = t, |t| ≤ 1 4t³ - t = 0 t(t² - 1) = 0 ⇒ t = 0 или t = ±1 2) Cosx = 0 ⇒ x = π/2 + πn, n ∈ Z Cosx = 1 ⇒ x = 2πk, k ∈ Z Cosx = -1 ⇒ x = π + 2πm, m ∈ Z Sinx*Sin(3x) + Sin(4x)*Sin(8x) = 0 Cos(2x) / 2 - Cos(4x) / 2 + Cos(4x) / 2 - Cos(12x) / 2 = 0 Cos(2x) / 2 - Cos(12x) / 2 = 0 |*2 Cos(2x) - Cos(12x) = 0 -2Sin(7x) • Sin(-5x) = 0 2Sin(7x) • Sin(5x) = 0 Sin(7x) = 0 или Sin(5x) = 0 Sin(7x) = 0 ⇒ 7x = πn ⇒ x = (πn)/7, n ∈ Z Sin(5x) = 0 ⇒ x = (πk)/5, k ∈ Z Другие два уравнения выставляй в другом вопросе