And we have a word for these points where the derivative is either 0 or the derivative is undefined. We call them critical points. So for the sake of this function, the critical points are, if we could include x sub 0, we could include x sub 1, at x sub 0 and x sub 1 the derivative is 0, and x sub 2 where the function is undefined. Now, so if we have a non-endpoint minimum or maximum point, then it's going to be a critical point. But can we say it the other way around? If we find a critical point where the derivative is 0 or the derivative is undefined, is that going to be a maximum or minimum point? And to think about that, let's imagine this point right over here.