Question

11 класс!Помогите решить уравнение $cos x+cos 2x+cos3x=0$

Answer 1

cosx + cos2x + cos3x = 0

cos2x + (cosx + cos3x) = 0

cos2x + 2 cos (3x + x / 2) cos (3x - x / 2) = 0

cos2x + 2 cos2xcosx = 0

cos2x (1 + 2cosx) = 0

cos2x = 0 или 1 + 2cosx = 0


вроде так