Well, let me write it in a more general notation, the way that you might be used to seeing it in your calculus book. It's telling us that if we want the area under the curve between two points, a and b, between two x points, a and b, of f of x. And so this is how we would denote the area under the curve between those two intervals. So let me draw that just to make it clear what I'm talking about in general terms. So this right over here could be f of x. And we care about the area under the curve between a and b. If we want to find the exact area under the curve, we can figure it out by taking the antiderivative of f. And let's just say that capital F of x is the antiderivative, or is an antiderivative, because you can have multiple that are shifted by constants, is an antiderivative of f. Then you just have to evaluate the antiderivative at the end points and take the difference.