x2-2x+3=6, x2-2x-3=0 is the stadard quadratic form in which a=1, b=-2 and c=-3.
x2-2x-3=(x-3)(x+1) so x=3 or -1 are the roots, because x-3=0, that is, x=3; or x+1=0, that is, x=-1.
The roots can also be found using the quadratic formula:
x=(-b±√(b2-4ac))/2a=(2±√(4-4×1×(-3)))/(2×1),
x=(2±√(4+12))/2=(2±√16)/2=(2±4)/2 which is (2+4)/2=6/2=3 or (2-4)/2=-2/2=-1.
So x=3 or -1 as before.