At x equals this, our derivative is equal to 0. Now, we know, I shouldn't say we're done yet. We don't know whether this is a minimum point. In order to figure out whether this is a minimum point, we have to figure out whether our function is concave upward or concave downward when x is equal to this business. And to figure that out, let's take the second derivative here. So the second derivative, so let me rewrite the second derivative of all of this business. The second derivative, well, this was the same function as this right over here.