Question

Решите уравнение
Cos5x-cos9x=0.

Answer 1

1)cos 5x - cos 9x = sin  2) cos x + cos 5x = 9 cos  3) cos x cos 9x = sin x sin 9x
4) sin 5x  = sin 9 x cos x  5)cos 5x cos x = cos 9x  6) cos x  + cos 9 x +cos 4 x =0