1) cos7x + cosx=0

2) sin²x - 3sinxcosx+2cos²x=0

3) 1+cosx+cos2x=0

1) cos4xcos3x=0

x=П/8 (2k+1) x=п/6 (2k+1)

2) tg^2x-3tgx+2=0

(3+-1) / 2

tgx=2 tgx=1

x=arctg2+Пk

x=П/4+Пk

3) cosx+2cos^2x=0 cosx (1+2cosx) = 0

x=П/2 (2k+1)

cosx=-1/2 x=П+-П/3+2 Пk

x=2 П/3+2 Пk

x=4 П/3+2 Пk