So let me do that. So I'll do it right over here. So f prime of a is equal to what by the definition of derivatives? Well, we could view that as the limit as x approaches a of f of x minus f of a over x minus a. So this is literally just the slope between two points. So if you have your function f of x like this, this is the point a, f of a right over here. This right over here is the point x, f of x.