[tex]\displaystyle x^2-2x-3=0 \\ a=1,b=-2,c=-3 \\ \Delta=b^2-4ac=2^2-4 \cdot 1 \cdot (-3)=4+12=16\ \textgreater \ 0 \\ x_1= \frac{2+ \sqrt{16} }{2 \cdot 1} = \frac{2+4}{2} = \frac{6}{2} =3 \\ \\ x_2= \frac{2- \sqrt{16} }{2 \cdot 1} = \frac{2-4}{2} = \frac{-2}{2} =-1[/tex]
