Question 886580
Visualizing that parabola, the inverse will be the lower half of the horizontal parabola.


Switching places f(x) and x just for easiness,
{{{x=y^2+3}}}
{{{y^2=x-3}}}
{{{y=0+-sqrt(x-3)}}}
You want {{{highlight(y=-sqrt(x-3))}}}.


{{{graph(-3,20,-10,3,-sqrt(x-3))}}}