A function could look something like this. A function could look something like this. And in this case, its absolute maximum is going to occur at the beginning of the interval. Or a function could look something like this. It could look something like that. And then the absolute maximum could occur at the end point of the interval, or the other possibility is that the function looks something like this, at which point the maximum would be at this critical point. And I say critical point as opposed to just a point where the slope is zero, because it's possible that the function is not differentiable there.