# Math Help - [SOLVED] Compound angle formulas - Finding exact values.

1. ## [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.
$tan(-\frac{7}{12}pi)$
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:

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

2. Note that $-\frac{7 \pi}{12} = -\frac{4 \pi}{12} - \frac{3 \pi}{12}$

So $tan(-\frac{\pi}{3}-\frac{\pi}{4}) = \frac{tan(-\frac{\pi}{3}) + tan(-\frac{\pi}{4})}{1-tan(-\frac{\pi}{3}) \cdot tan(-\frac{\pi}{4})} = \frac{-1 -\sqrt{3}}{1-\sqrt{3}}$