Question

3cos^2× - 5 sin^2× - sin2x = 0

помогите пожалуйста 

Answer 1

3cos^2x/cos^x-5sin^2x/cos^2x+2sinxcosx/cos^2x=0
3-5tg^2x-2tgx=0
5tg^2x+2tgx-3=0
Tgx=t
D=64=8
T1=3/5
T2=-1
Tgx=-1
X=-п/4+пn
Tgx=3/5
X=arctg3/5+пn