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. n choose 1 of x to the n minus 1 delta x plus n choose 2 x to the n minus 2 delta x squared. And then plus, and we have a bunch of digits. And in this proof, we don't have to go through all the digits, but the binomial theorem tells us what they are.