I need to know how to get this part.

Here's the problem:

Now it's obvious that you can use the product rule to differentiate the three of these, which I've done.

It'll look something like this:

However, on the last part, I'm only able to get 2 parts of the answer. The

and

are kept constant while I'm having trouble differentiating the

:

When seemed obvious to me was that you'd bring the power of 2 to the outside and then differentiate, which would lead to

but this is not the answer in the back of the book.

is supposed to be =

I had four tutors working on this problem who gave up on it at my college, which I thought was either sad or Michael Spivak (author of this legendary Calculus text) made an error.