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. So when does this thing equal zero? So when does 2x minus 512 x to the negative 3 equal zero? Well, we can add 512 x to the negative 3 to both sides, so you get 2x is equal to 512 x to the negative 3rd power.