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. I like to just think of this as the rate at which x is changing with respect to y is zero. And so that got us to the same conclusion. Well, for that to be true, x has to be equal to three y squared.