It is 0 here and here. So we would call those critical points. I don't see any undefined, any points at which the derivative is undefined just yet. 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.