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Math Help - Law of cosine and sine

  1. #1
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    Law of cosine and sine

    Hi,

    The three sides of the triangle being a, b and c.

    1. Can anyone get me the derivation of the law of cosine.
    c=a^2+b^2-(2ab cos \theta)

    2. Also, the law of sine.

    (sin A)/a = (sin B)/b = (sin C)/c

    where,
    A, B and C are the internal angles subtended by the sides of the triangle a, b and c respectively.
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  2. #2
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    Quote Originally Posted by willki View Post
    Hi,

    The three sides of the triangle being a, b and c.

    1. Can anyone get me the derivation of the law of cosine.
    c=a^2+b^2-(2ab cos \theta)

    2. Also, the law of sine.

    (sin A)/a = (sin B)/b = (sin C)/c

    where,
    A, B and C are the internal angles subtended by the sides of the triangle a, b and c respectively.
    You'll find six proofs of the cosine rule here, and a discussion of the sine rule here.
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