But what's going to be interesting, and it's really one of the foundational ideas of calculus, is, well, what happens as these points get closer and closer together? We found the average rate of change between one and three, or the slope of the secant line from one comma one to three comma nine. But what instead if you found the slope of the secant line between two comma four and three comma nine? So what if you found this slope? But what if you wanted to get even closer? Let's say you wanted to find the slope of the secant line between the point 2.5, 6.25, and three comma nine. And what if you just kept getting closer and closer and closer?