Cos3x+cos2x+cosx=0Решите плиз

Question

Cos3x+cos2x+cosx=0
Решите плиз

Answer 1

4cos³x-3cosx+2cos²x-1+cosx=0
4cos³x+2cos²x-2cosx-1=0
(2cosx+1)*(2cos²x-1)=0
x=+-П/6+2Пn;
х=-п/4+2Пn;
х=п/4+2Пn;