2) cos²x – 3sinxcosx-1;

: cos^2x-3sinxcosx=-1

cos^2x-3sincos+sin^2+cos^2=0

2cos^2+sin^2-3sincos=0

2+tg^2-3tg=0

D=1

X1,2 = 2; 1

tgx=2 tgx=1

x=arctg2+pk x=p/4+pk

x=p-arctg2+pk