We know that at x is equal to 1, let me write it over here. We figured out at x is equal to 1, the slope is 0. So f prime prime is, sorry, let me write it this way. I should have said, we know that the slope is 0. Slope is equal to 0, and we figured that out because the first derivative was 0. This was a critical point. And we know that we're dealing with, the function is concave upwards at this point.