You're going to be left with this area right over here. So what's another way of writing that? Well, another way of writing this area right over here is the definite integral between x and x plus delta x of f of t dt. So we can rewrite this entire expression, the derivative of capital F of x. This is capital F prime of x. We can rewrite it now as being equal to the limit as delta x approaches 0. This I can write as 1 over delta x times the numerator.