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. And so let me color code it. So that is the same thing as that, and that is the same thing as that. And you wouldn't even have to use the product rule here.