Well, f of x here is just x to the n. All of that over delta x. And now that we know the binomial theorem, we can figure out what the expansion of x plus delta x is to the nth power. And if you don't know the binomial theorem, go to my pre-calculus playlist and watch the videos on the binomial theorem. So the binomial theorem tells us that this is equal to, and let me, I'm going to need some space for this one, the limit as delta x approaches 0. And what's the binomial theorem tell us? This is going to be equal to, I'm just going to do the numerator, x to the n plus n choose 1. And once again, review the binomial theorem if this looks like Latin to you and you don't know Latin.