I was hoping someone would look at the following question for me. I have tried to derive equation 1 below (the show derivation link isn't working so i can't check) in their solution below. I have scanned in my working out. When i did the problem i got the correct answer a totally different way so I wanted to check i could do it their way too.
It might look a lot but it will only take you experts a couple of minutes I'm sure :)