I am rather confused as to how to go about doing this problem.
Evaluate using formulas developed in this section.
That is how it is shown in the question. *The formulas being referred to are the compound angle formulas*
What is confusing me is why the pi is on the outside of the fraction. I do not know how to start it. If you could just show how to get it into one of the compound angle formulas I could likely take it from there.
The answer shown in the book is: