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Math Help - Semi-Advanced Cos Question

  1. #1
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    Semi-Advanced Cos Question

    If x = 7pi/15 is a solution to the equation cos(x)=B, where B is some constant, then what must B be equal to?
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  3. #3
    Senior Member pacman's Avatar
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    7pi/15 = (7pi/15)(180/pi) = 7(12) = 84 degress

    cos 7pi/15 = cos 14pi/30 = sin (pi/2 - 14pi/30) = sin pi/30 = sin 6 degrees

    cos 7pi/15 = sin pi/30 = sin 6 degrees = -(1/8)(1 + sqrt 5 - sqrt(6(5 - sqrt 5))) = 0.1045285
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