I have a problem with derivative.Sorry,my topic is abit off :P,not use to doing this stuff at the computer.
The book says that the right answer is
Now you have to find . Do that in the same way, putting , where , and using the chain rule to find in terms of . Then use the chain rule once more to find . Finally, put everything together into a single expression and simplify it.
BTW this is a classic example of a case where using parentheses correctly makes things much easier to read: looks like a jumble, but is a lot clearer.