So as x gets closer and closer and closer and closer to a, what's going to happen is that when x is out here, we have this secant line. We're finding the slope of this secant line. But as x gets closer and closer, the secant lines better and better and better approximate the slope of the tangent line. Where the limit as x approaches a, but doesn't quite equal a, is going to be, this is actually our definition of our derivative, or I guess the alternate form of the derivative definition. And this would be the slope of the tangent line, if it exists. So with all that out of the way, let's try to answer their question. With the alternative form of the derivative as an aid, make sense of the following limit expression by identifying the function f and the number a.