But you actually have cases where your derivative, your first derivative is zero, but you don't have an extremum. So for example, you could have a point like this, where right over here, your slope or your derivative could be equal to zero, and so your first derivative would be equal to zero, but notice, your slope is positive, it hits zero, and then it goes back to being positive again. And so you can't make the conclusion just because your derivative is zero that it's definitely an extremum. You could say it's a critical point, and so step two is correct. In order to make this conclusion, you would have to test what the derivative is doing before that point and after that point, and verify that it is switching sides. And we could try to do that. So let's make a little table here.