In general, at 0, as we're near 0 from either direction, we're going to be concave upwards. The fact that 0 is a critical point, and that we're always concave upward as we approach 0 from either side, this tells us that this is a minimum point. Because we're concave upwards all around 0. 0 is not an inflection point. Let's see if positive and negative 3 are inflection points. If you study this equation, let me write our... Actually, I just want to be clear. I've just been using the numerator of the second derivative.