So every term, this first term has no delta x in it, but every other term does. Every other term, even after we divide it by delta x, has a delta x in it. So that's a 0. Every term is 0. All of the other, I don't know, what is it, n minus 1 terms, they're all 0. So all we're left with is that this is equal to n choose 1 of x to the n minus 1. And what's n choose 1?