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

  1. #1
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    [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}}
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  2. #2
    Senior Member Twig's Avatar
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    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}}
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