f(x)=x^2-2x-3 is defined for all Real values of x
therefore the Domain of f(x) covers all Real values (i.e. x in RR)
x^2-2x-3 can be written in vertex form as (x-color(red)1)^2+color(blue)((-4)) with vertex at (color(red)1,color(blue)(-4))
Since the (implied) coefficient of x^2 (namely 1) is positive, the vertex is a minimum
and color(blue)((-4)) is a minimum value for f(x);
f(x) increases without bound (i.e. approaches color(magenta)(+oo)) as xrarr +-oo
so f(x) has a Range of [color(blue)(-4),color(magenta)(+oo))
