as you may know, to get the "inverse relation" of any expression, we start off by doing a quick switcharoo on the variables, and then we solve for "y".
[tex]\bf \stackrel{f(x)}{y}=\sqrt{x-5}\qquad \boxed{x}=\sqrt{\boxed{y}-5}\impliedby \textit{let's square both sides}
\\\\\\
(x)^2=(\sqrt{y-5})^2\implies x^2=y-5\implies x^2+5=\stackrel{f^{-1}(x)}{y}[/tex]
