2cos^2(3x)+cos(3x)+cos(9x)=1

2cos^2(3x)-1=2cos^2(3x)-cos^2(3x)-sin^2(3x)=cos^2(3x)-sin^2(3x)=cos6x       тогда 2cos^2(3x)-1+cos(3x)+cos(9x)=0 cos(6x)+cos(3x)+cos(9x)=0 cos(6x)+2cos(3x+9x)/2*cos(9x-3x)/2=0 cos(6x)+2cos(6x)*cos(3x)=0 cos(6x)(1+2cos(3x))=0 1)cos(6x)=0                                           2)1+cos(3x)=0    6x=п/2+2пk                                             cos(3x)=-1    x=п/12+пk/3                                           3x=п+2пk                                                                   x=п/3+2/3пк