So this is the derivative of y with respect to x. If we take the reciprocal of that, the derivative of x with respect to y, just the reciprocal of this, is going to be the reciprocal of what we have here. So it's going to be three y squared minus x over y. 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.