So the derivative, s prime, let me do this in a different color, s prime of x, I'll do it right over here, actually. The derivative, s prime of x, with respect to x, is going to be equal to 2x times negative 2 times 5, 2x plus 256 times negative 2, so that's minus 512 x to the negative 3 power. X to the negative 3 power. Now, this is going to be undefined, this is going to be undefined when x is equal to zero, but if x is equal to zero, then y is undefined, so this whole thing breaks down. So that isn't a useful critical point, x equals zero. So let's think about any other ones. Well, it's defined everywhere else, so let's think about where the derivative is equal to zero.