So let's review how we can identify concave downward intervals and concave upwards intervals. So if we're talking about concave downwards, we see several things. We see that the slope is decreasing, which is another way of saying that f prime of x is decreasing, which is another way of saying that the second derivative must be negative. 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.