sin^3 x - sin^2 x cos x + 2cos^3 x = 0 /:cos^3 x≠0
tg^3x - tg^2x +2 =0
замена tgx=t
t^3 - t^2+2=0
(t+1)(t^2 -2t+2)=0
t=-1⇒tgx= -1⇒ x= - pi/4+pik, k∈Z
