23D.cos (1.5 п+2x )= cos x cos 2 x= cos x cos^2 x - sin^2 x= cos x
cos^2 x - ( 1- cos^2 x ) = cos x 2 cos^2 x - cos x - 1 = 0
D= 1-4*2*1 = 1+8=9 = 3^2 ( cos x)1= (1-3)/4= - 1 /2 (cos x)2=(1+3)/4=1
(cos x)1= - 1/2 x1=(+ , -)arc cos (-1/2) + 2 П*n = (+,- ) (-П/3)+2П*n
(cosx)2=1 x2= 2П *k