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Math Help - [SOLVED] Given sin (pi/6)=1/2 use an equivalent trig expression to show cos 2pi/3=-1/

  1. #1
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    [SOLVED] Given sin (pi/6)=1/2 use an equivalent trig expression to show cos 2pi/3=-1/

    which cofunction identities would u use
    cos (x+pi/2)=-sinx or sin (x+pi/2)=cosx? how did u determine which one to use?
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  2. #2
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    Quote Originally Posted by jepal View Post
    which cofunction identities would u use
    cos (x+pi/2)=-sinx or sin (x+pi/2)=cosx? how did u determine which one to use?
    What you use will probably vary with your personal preference and the context. Did you have some particular exercise in mind?
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  3. #3
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    Quote Originally Posted by stapel View Post
    What you use will probably vary with your personal preference and the context. Did you have some particular exercise in mind?
    here:

    sin (pi/6)=1/2 use an equivalent trig expression to show cos 2pi/3=-1/2
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  4. #4
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    Quote Originally Posted by jepal View Post
    here:

    sin (pi/6)=1/2 use an equivalent trig expression to show cos 2pi/3=-1/2
    \sin (\frac{\pi}{6}) = \frac{1}{2}

    \sin (\theta) = \cos (\frac{\pi}{2} - \theta)

    Hence, \cos (\frac{\pi}{3}) = \frac{1}{2}

    Also, \cos (\pi - \theta) = -\cos (\theta)

    Therefore, \cos(\frac{2\pi}{3}) = \cos (\pi - \frac{\pi}{3}) = -\cos (\frac{\pi}{3}) = -\frac{1}{2}
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  5. #5
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    solved

    ignore this question....i got the answer.
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