Cos2x=1-cos(пи на 2-x)

cos(pi/2 - x) = sin x cos 2x = 1 - 2sin^2 x Подставляем 1 - 2sin^2 x = 1 - sin x 0 = 2sin^2 x - sin x sin x*(2sin x - 1) = 0 1) sin x = 0; x1 = pi*k 2) sin x = 1/2; x2 = pi/6 + 2pi*k; x3 = 5pi/6 + 2pi*k