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Math Help - Find exact sine value

  1. #1
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    Find exact sine value

    Quote Originally Posted by Another user. Dont ask.
    I need to find the exact value of sin(π/16) without using a calculator. I thought that to do this I have to use the formula: sin(A+-B) = sinAcosB+-cosAsinB but I can't find the correct two angles that add up to π/16 from all the angles on the unit circle. Thanks for any help.
    ..
    Last edited by mr fantastic; April 20th 2009 at 01:45 AM. Reason: This question was posted by another user whose name I felt might offend some members.
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  2. #2
    MHF Contributor red_dog's Avatar
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    You can use this: \sin\frac{x}{2}=\sqrt{\frac{1-\cos x}{2}} and \cos\frac{x}{2}=\sqrt{\frac{1+\cos x}{2}}

    \sin\frac{\pi}{16}=\sqrt{\frac{1-\cos\frac{\pi}{8}}{2}}

    \cos\frac{\pi}{8}=\sqrt{\frac{1+\cos\frac{\pi}{4}}  {2}}
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  3. #3
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    Thread closed.
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