He shouldn't have just taken the product of the derivatives, he should have applied the product rule. So his work is not correct, and his mistake is that he didn't apply the product rule. He just assumed that the derivative of the products is the same thing as the product of the derivatives. Let's do more examples. Okay, so let's see. It says, Katie tried to find the derivative of two x squared minus four, all of that to the third power. Here is her work.