So even when we take the slopes between two points on the line, the secant lines, you can see that those slopes are changing. But what if we wanted to ask ourselves an even more interesting question? What is the instantaneous rate of change at a point? So for example, how fast is y changing with respect to x exactly at that point, exactly when x is equal to that value? Let's call it x one. Well, one way you could think about it is what if we could draw a tangent line to this point, a line that just touches the graph right over there? And we can calculate the slope of that line.