### Video Summary:

A function f is a one-to-one function if, for elements a and b from the domain of f, a b implies f (a) f (b). Only functions that are one-to-one have inverses. If every horizontal line intersects the graph of a function at no more than one point, then the function is one-to-one. Notation for the inverse function f -1 is read “f-inverse”. By the definition of inverse function, the domain of f equals the range of f -1, and the range of f equals the domain of f -1.