This is going to be equal to, it's going to be the limit, and I'm just applying the property of limit, property, I'm applying a property of limits here. So the limit of the product is equal to the same thing as the product of the limits. So it's the limit as x approaches C of x minus C times the limit, let me write it this way, times the limit as x approaches C of f of x minus f of C. All of that over x minus C. Now what is this thing right over here? Well if we assume that f is differentiable at C, and we're going to do that, actually I should have started off there. Let's assume, let's assume, because we wanted to show that differentiability improves continuity. If we assume f differentiable, differentiable at C, well then this right over here is just going to be f prime of C. This right over here, we just saw it right over here, that's this exact same thing. This is f prime, f prime of C. And what is this thing right over here?