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Math Help - laws of sine and cosine

  1. #1
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    laws of sine and cosine

    Explain why itis dangerous to use the law of sines to find the size of an unknown angle in a triangle, but it is not dangerous to use the law of cosines. be discriptive and use examples? This one really stumped me if u could help that would be great thanks
    Last edited by ksizzle; September 23rd 2008 at 06:39 PM. Reason: spelling error
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  2. #2
    MHF Contributor
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    The law of sines relates the lengths of sides with the sines of their opposite angles. It is dangerous to calculate angles using the law of sines because if you are given 2 sides and an angle opposite one of those sides, you cannot tell if the angle opposite the second side will be greater or less than \frac{\pi}{2}. Since \sin{x} = \sin{(\pi - x)}, you can't tell which angle is correct simply with that information.
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