And let's see, over here it looks like she's taking the derivative of the entire expression with respect to the inner expression. And that is close to applying the chain rule properly, but it's not applying the chain rule properly. So her work is not correct, and her mistake is she's not correctly applying the chain rule. Just as a review, the chain rule says, look, if we're trying to take the derivative with respect to x of f of g of x, f of g of x, f of g of x, that this is going to be equal to, this is going to be equal to the derivative of the whole thing with respect to g of x. So I could write that as f prime of g of x, f prime of g of x, times the derivative of the inner function with respect to x, times g prime of x. So over here, we could view our f function as a thing that takes its input and takes it to the third power. And so this right over here is f prime of g of x.