Answer
$f^{-1}(x)=x^2+2$
Work Step by Step
$f(x)=\sqrt{x-2},$
$y=\sqrt{x-2},$
$x=\sqrt{y-2},$
$x^2=\sqrt{y-2},$
$y=x^2+2=f^{-1}(x),$
Checking the inverse function..
$(f\circ f^{-1})(x)=\sqrt{x^2+2-2}=\sqrt{x^2}=x$
$(f^{-1}\circ f)(x)=(\sqrt{x-2})^2+2=x-2+2=x$