Cosx+2cos2*x=0 Помогите

Question

Cosx+2cos2*x=0
Помогите

Answer 1

cosx+cos2x=0.  

cosx+2cos²x-1=0  

пусть cosx=t; |t|≤1  

2t²+t-1=0  

t1=-1  

t2=1/2  

a) cosx=-1  

x=π+2πn  

б) cosx=1/2  

x=±π/3+2πn