( 1 - 8 sin x/3 cos 2/3 ) =0
(1-8sin x/3 cos x/3)=0 -4*2sin x/3 cos x/3=-1 sin(2x/3)=1/4 2x/3=(-1)^n arcsin(1/4) +πn, n-celoe x=(-1)^n *(3/2arcsin1/4) +3/2 *πn