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Math Help - basic trigo

  1. #1
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    jamshedpur
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    basic trigo

    Prove that
    cos a +cos b +cos c + cos (a + b+ c) = 4 cos ((a+b)/2) ((b+c)/2) ((c+a)/2)
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  2. #2
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    Re: basic trigo

    Sorry it is
    cos a +cos b +cos c + cos (a + b+ c) = 4 cos ((a+b)/2) cos ((b+c)/2) cos ((c+a)/2)
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  3. #3
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    Re: basic trigo

    please post the effort you have made on this question
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