And let me be clear. Capital F of x is differentiable at every possible x between c and d, and the derivative of capital F of x is going to be equal to lowercase f of x. Fair enough. Now what I wanna do in this video is connect the first fundamental theorem of calculus to the second part, or the second fundamental theorem of calculus, which we tend to use to actually evaluate definite integrals. So let's think about, let's think about what f of, f of b, what f of b minus f of a is, what this is, where both b and a are also in this interval. So f of b, and we're gonna assume that b is larger than a. So let's say that b is this right over here.