3cos2x+10sin*2x-6=0
3(cos^2x-sin^2x)+20sinxcosx-6(sin^2x+cos^2x)=0
3cos^2x-3sin^2x+20sinxcosx-6sin^2x-6cos^2x=0
9sin^2x-20sinxcosx+3cos^2x=0 /:cos^2x≠0
9tg^2x-20tgx+3=0
tgx=t
D=400-108=292
t=(20+2√73)/18=(10+√73)/9
t=(20-2√73)/18=(10-√73)/9
tgx=(10+√73)/9
x=arctg(10+√73)/9+pik, k∈Z
tgx=(10-√73)/9
x=arctg(10-√73)/9+pik, k∈Z