So we would call here and here critical points. So these are candidate minimum, these are candidate points at which our function might take on a minimum or a maximum value. And the way that we figured out whether there was a minimum or maximum value is to look at the behavior of the derivative around that point. And over here, we saw the derivative is positive as we approach that point. And then it becomes negative. It goes from being positive to negative as we cross that point, which means that the function was increasing. If the derivative is positive, that means that the function was increasing as we approached that point, and then decreasing as we leave that point, which is a pretty good way to think about this being a maximum point.