5tg^2(x)+13tg(x)=6
tg(x)=y
5y^2+13y-6=0
D=13^2-4*5*(-6)=169+120=289
y1= (-13+17)/2*5=4/10=0.4
y2=(-13-17)/2*5=-30/10=-3
tg(x)=0.4 x=+/- arctg(0.4)+Pi*n, n-целое
tg(x)=-3 x=+/- arctg(-3)+Pi*n, n-целое
