You're going to get the definite integral from a to x plus delta x of f of t dt. And then from that, you are going to subtract this business, f of x, which we've already written as the definite integral from a to x of f of t dt. And then all of that is over delta x. Now, what does this represent? Remember, we don't know anything about definite integrals or somehow dealing with something with an antiderivative and all that. We just know this is another way of saying the area under the curve f between a and x plus delta x. So it's the area under the curve f between a and x plus delta x.