Well, remember, we're taking the limit as delta x approaches 0. So as delta x approaches 0, pretty much every term that has a delta x in it, it becomes 0, right? We just, when you multiply by 0, you get 0. 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.