This is the right answer. Now, so his work is correct. He did not make any mistakes, but I do have a bone to pick, so to speak, with Tom, because he didn't have to apply the quotient rule here. He did all of this hairy calculus and algebra, but there could have been a very simple simplification he could have made up here, and this is a key thing to realize. He could have said, hey, you know what? This is the same thing as the derivative with respect to x of x to the 1.5, that's what the square root of x is, times x to the negative fourth power. That's what one over x to the fourth is.