We already know that the derivative of y with respect to x is equal to two x minus y. Now to find the second derivative, I just want to take the derivative of both sides of this with respect to x. So let's do that. So I could take the derivative of the left-hand side with respect to x, and the derivative of the right-hand side with respect to x. And so what is this going to be? On the left-hand side, the notation would just be the second derivative of y with respect to x. And then over here, let's take the derivative of each of these with respect to x.