It connects differential calculus and integral calculus. Connection between derivatives, or maybe I should say antiderivatives, and integration, which before this video we just viewed integration as area under curve. Now that we see it has a connection to derivatives. Well, how would you actually use the fundamental theorem of calculus? Well, maybe in the context of a calculus class. And we'll do the intuition for why this happens or why this is true and maybe a proof in later videos. But how would you actually apply this right over here?