From the 2009 HSC 4u paper...why don't you read some of the worked solutions available online? There's so many these days. This question looks hard, but it's pretty easy if you use the identity derived in part i). Oh yeah, you should probably include that as well, because to do it without it is impossible.
http://www.hsccoaching.com/Resources/2009 Ext1.pdf
See Q8, part a.