This is his solution. And then later we are asked, is Robert's work correct? If not, what's his mistake? So pause this video and try to figure it out on your own. All right, now let's work through this together. So our original g of x is equal to the cube root of x, which is the same thing as x to the 1 3rd. So in step one, it looks like Robert's trying to find the first and second derivative.