And now just to clarify something, and sometimes you'll see it in different calculus books, sometimes instead of an h, they'll write a delta x here, where this second point would have been defined as x naught plus delta x. And then this would have simplified to just delta x over there, and we'd be taking the limit as delta x approaches 0. The exact same thing. h delta x doesn't matter. We're taking h as the difference between one x point and then the higher x point, and then we're just going to take the limit as that approaches 0. We could have called that delta x just as easily. But I'm going to call this thing, which we're saying it equals the slope of the tangent line, and it does equal the slope of the tangent line, I'm going to call this the derivative of f. Let me write that down.