Question

1) cos7x+ cosx=0
2) sin²x- 3sinxcosx+2cos²x=0
3) 1+cosx+cos2x=0

Answer 1

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+2Пk
x=2П/3+2Пk
x=4П/3+2Пk