The issue with finding the inverse of x=2 is that x=2 isn't a function. A function is an ordered tuple from one set to another. x=2 only refers to an one element of one set. Furthermore, if you want your function to have an inverse the rule has to have other requirements. It has to be bijective, which means it has to be both injective and surjective. Hence [tex]y = x^3-x[/tex]
has no inverse since solving for x gives multiple functions.