And so now we have an approximation. Or we could say, look, the area of each of these rectangles are going to be f of x sub i, or maybe x sub i is the right boundary the way I've drawn it, times delta x i. That's each of these rectangles. And then we can sum them up. And that would give us an approximation for the area. But as long as we use a finite number, we might say, well, we can always get better by making our delta x's smaller, and then by having more of these rectangles. Or get to a situation, here we're going from i is equal to one to i is equal to n. But what happens is delta x gets thinner and thinner and thinner, and we have, and n gets larger and larger and larger.