[latex]cos^2x-3sinxcosx=-1\cos^2x-3sinxcosx=-sin^2x-cos^2x |:cos^2x\1-3tgx=-tg^2x-1\tg^2x-3tgx+2=0\tgx=t\t^2-3t+2=0\ t_{1,2}= frac{3 ^+_- sqrt{9-8} }{2} =frac{3 ^+_- 1}{2} = left { {{t_1=1} atop {t_2=2}} ight.\ 1)tgx=1 \ x= frac{ pi}{4}+ pi n, n o Z \ 2)tgx=2\x=arctg2+ pi k, k o Z[/latex]