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Math Help - Need help with a double angle question

  1. #1
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    Need help with a double angle question

    If cos2x=12/13 and 2x is in the first quadrant, evaluate the six trigonometric functions for x, without your calculator. The answer is:

    cos x= 5/√26; sec x=√26/5

    sinx=1/
    √26; csc x=√26

    tanx=1/5; cot x=5

    How do I get these answers? Any help would be greatly appreciated.
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  2. #2
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    Re: Need help with a double angle question

    Do you know either the "double angle formulas" or the "half angle formulas"?
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  3. #3
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    Re: Need help with a double angle question

    since 0 < 2x < \frac{\pi}{2} , then 0 < x < \frac{\pi}{4}

    \cos{x} = \sqrt{\frac{1 + \cos(2x)}{2}}

    \sin{x} = \sqrt{\frac{1 - \cos(2x)}{2}}

    sub in the value given for \cos(2x) ...
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  4. #4
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    Re: Need help with a double angle question

    Thanks guys, I got it now.
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