Notice, as we approach from the left-hand side, the slope looks like a constant, I don't know, it looks like a positive 3 1⁄2. Well, as we go to the right side of that, it looks like our slope turns negative. And so if you were to try to find the limit of the slope as we approach from either side, which is essentially what you're trying to do when you try to find the derivative, well, it's not going to be defined because it's different on either side. So f is also not differentiable at the x value that gives us that little sharp point right over there. And if you were to graph the derivative, which we will do in future videos, you will see that the derivative is not continuous at that point. So let me mark that off. And then we could check x equals zero.