Or we could have a maximum point someplace in between that looks like this. And if it looks like this, then here the derivative would be undefined. So we have a couple of different tangent lines that you could place right over there. So what we need to do is let's test the different endpoints. Let's test the function at the beginning. Let's test the function at the end of the interval. And then let's see if there's any points where the derivative is either zero or the derivative is undefined.