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Math Help - cosine question

  1. #1
    Senior Member euclid2's Avatar
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    cosine question

    if two sides between the contained angle are 15 and 30 where the contained angle is 20, is the length of the other side 16.7 or 14.5?
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  2. #2
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    16.7

    Use the cosine rule. Let A denote the contained angle, a denotes side opposite angle A, and b and c are the remaining two sides.

    a^2 = b^2 + c^2 - 2bc\cos{A}

    a^2 = 1125 - 900\cos{20}

    a = \sqrt{1125 - 900\cos{20}} \approx 16.71157208
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