And if we want this to be equal to zero, like we said right over here, well, then that's only going to happen if the numerator is equal to zero. So we can say, okay, at what xy pair does this numerator equal to zero? Three y squared minus x is equal to zero. You can add x to both sides, and you get three y squared is equal to x. Now another way you could have thought about it is, well, at what x and y values does the derivative of y with respect to x become undefined? Well, that's going to become undefined if the denominator here is zero. But when you're dealing with things like undefined, it gets a little bit more hand-wavy.