So that is equal to, let me, the limit as delta x approaches 0 of, so we divide the top and the bottom by delta x, or we multiply the numerator times 1 over delta x, we get n choose 1 x to the n minus 1. What's delta x divided by delta x? Well, that's just 1, right? Plus n choose 2 x to the n minus 2. This is delta x squared, but when we divide by delta x, we just get a delta x here. And then we keep having a bunch of terms. We're going to divide all of them by delta x, right?