[SOLVED] Compound angle formulas - Finding exact values.

I am rather confused as to how to go about doing this problem.

Evaluate using formulas developed in this section.

$\displaystyle tan(-\frac{7}{12}pi) $

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:

$\displaystyle -\frac{1 + \sqrt{3}}{1 - \sqrt{3}} $