And then let's see if there's any points where the derivative is either zero or the derivative is undefined. And these points where the derivative is either zero or it's undefined, we've seen them before, we call these, of course, critical numbers. And this would be either in either case, actually if we assume that that's happening at the same number, we would call that a critical number. So those are the different candidates. Now you could have a critical number in between where, say, the slope is zero, say something like this, but it isn't the maximum or minimum. But what we can do is if we can find all the critical numbers, we can then test the function evaluated at the critical numbers and the function evaluated at the endpoints, and we can see which of those are the largest. All of those are the possible candidates for where f hits a maximum value.