So let's think about what they're saying. So we're looking for a place where the first derivative is greater than zero. That means that the slope of the tangent line is positive. That means that the function is increasing over that interval. So if we just think about it here, over this whole region right over here, the function is clearly decreasing. Then the slope becomes zero right over here. And then the function starts increasing again, all the way until this point right over here.