Let me draw another diagram here. So let's say that's my y-axis, this is my x-axis, this is my function. As n approaches infinity, so this is a, this is b, you're just going to have a ton of rectangles. You're just going to get a ton of rectangles over there and they're going to become better and better approximations for the actual area. And the actual area under the curve is denoted by the integral from a to b of f of x times dx. And just to make it, you see where this is coming from, or how these notations are close, or at least in my brain, how they're connected, delta x was the distance for each of these, was the width for each of these sections. This right here is delta x, so that is a delta x.