And we call that slope of the tangent line, we call that the derivative at x equals C. We say that this is going to be equal to f prime of C. All of this is review. So if we're saying, one way to think about it, if we're saying that the function f is differentiable at x equals C, we're really just saying that this limit right over here actually exists. And if this limit actually exists, we just call that value f prime of C. So that's just a review of differentiability. Now let's give ourselves a review of continuity. Con-ti-nuity. So the definition for continuity is if the limit as x approaches C of f of x is equal to f of C. Now this might seem a little bit, you know, well, it might pop out to you as being intuitive, or it might seem a little, well, where did this come from? Well, let's visualize it, and then hopefully it'll make some intuitive sense.