So this is going to be the derivative of g with respect to f of x, so that's going to be g prime of f of x, g prime of f of x, times the derivative of f of x with respect to x, so times f prime of x, and then that is going to be equal to what? Well, the derivative with respect to x of x, that's just equal to one. And this is where we get our interesting result. All we did so far is we used something we knew about inverse functions, and we used the chain rule to take the derivative of the left-hand side, but if you divide both sides by g prime of f of x, what are you going to get? You're going to get a relationship between the derivative of a function and the derivative of its inverse. So you get f prime of x is going to be equal to one over all of this business, one over g prime of f of x, g prime of f of x. And this is really neat, because if you know something about the derivative of a function, you can then start to figure out things about the derivative of its inverse.