In the usual sense, it has no inverse function. Since it is not an injection (f(0)=f(2)=0), an inverse function would have to map 0 both to 0 and 2, and that’s impossible.
However, if you restrict the domain to [1,+oo> (to make it injective), and the codomain to [-1,+oo> (to make it surjective), then it has an inverse function, given by g(y)=1+sqrt(y+1).
