Well, there would be two tangent lines that are horizontal based on how I've drawn it. One might be right over there, so it might be like there, and then another one might be maybe right over here. And they want the equation of the horizontal line that is tangent to the curve and is above the x-axis. So what do we know, what is true if this tangent line is horizontal? Well, that tells us that at this point, dy dx is equal to zero. In fact, that would be true at both of these points. And we know what dy dx is.