If the first derivative is decreasing, the second derivative must be negative, which is another way of saying that the second derivative over that interval must be negative. So if you have a negative second derivative, then you are in a concave downward interval. Similarly, I have trouble saying that word. Let's think about concave upwards, where you have an upward opening u. Concave upwards, in these intervals, the slope is increasing. We have a negative slope, less negative, less negative, 0, positive, more positive, more positive, even more positive. So slope is increasing, which means that the derivative of the function is increasing. And you see that right over here.