3x³ - 2x² + 9x - 6 = (3x³ - 2x²) + (9x - 6) = x²(3x - 2) + 3(3x - 2) =
= (3x - 2)(x² + 3)
Сosa=15/17,sina=√(1-225/289)=√64/289=8/17,tga=8/17:15/17=8/15
cosb=1/4;sinb=√(1-1/16)=√15/16=√15/4,tgb=√15
tg(a+b)=(tga+tgb)/(1-tgatgb)=(8+15√15)/(15-120√15)
tg(a-b)=(tga-tgb)/(1+tgatgb)=(8-15√15)/(15+120√15)
tg2a=2tga/(1-tg²a)=16/15:(1-64/225)=240/181
tg2b=2tgb/(1-tg²b)=-√15/7
(4-5х)=5х-4
4-5х=5х-4
8=10х
х=0,8