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Math Help - Trig

  1. #1
    Newbie
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    Nov 2009
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    Trig

    If A,B, and C are angles in a triangle prove that sin B=sin(A+C).
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  2. #2
    Member Black's Avatar
    Joined
    Nov 2009
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    If A, B, and C are angles in a triangle, then A + B + C = 180 deg

    So

    sin(B) = sin(180 - (A + C))
    = sin(180)cos(A + C) - cos(180)sin(A + C) (Double-Angle formula)

    = sin(A + C). (sin(180) = 0 & cos(180) = -1)
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