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. So right here, they want to find the slope of the tangent line at 5. Here, they wanted to find the slope of the tangent line at a. So it's pretty clear that a is equal to 5 and that f of a is equal to 125.