But that is not true if we are dealing with the product of functions. The derivative with respect to x of f of x, g of x, is not necessarily, maybe there's some very special circumstances, but in general, it's not going to be just the product of the derivative. It's not going to be just f prime of x, g prime of x. Here we would want to apply the product rule. This is going to be equal to, this is going to be equal to the derivative of the first function times the second function, plus the derivative, well let me write it this way, plus the first function, not taking its derivative, times the derivative of the second function. So he should have applied the product rule here. And so let's do that, just to see what his answer should have been.