And we can calculate the slope of that line. Well, that should be the rate of change at that point, the instantaneous rate of change. So in this case, the tangent line might look something like that. If we know the slope of this, well, then we could say that that's the instantaneous rate of change at that point. Why do I say instantaneous rate of change? Well, think about the video on the sprinters, the Usain Bolt example. If we wanted to figure out the speed of Usain Bolt at a given instant, well, maybe this describes his position with respect to time.