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Math Help - Sine and Cosine rules

  1. #1
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    Sine and Cosine rules

    Hello Everyone,
    I would really appreciate if someone could help me with this question.

    In a triangle ABC, c=7, b=8 and C=60degrees
    (a) Use Cosine rule to write down a quadtratic equation involving a
    (b) Hence solve it
    (c) Use Sine rule to find two values of a(first find B and so A) and compare these with your answers in part(b)

    I have no idea what the question really means. Any sort of help would be really appreciated
    Thank you in advance
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  2. #2
    Super Member craig's Avatar
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    Just to help you along a bit, here is the Sine rule for triangle abc with angles A, B, C:

    \frac{a}{\sin{A}} = \frac{b}{\sin{B}} = \frac{c}{\sin{C}}
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  3. #3
    A riddle wrapped in an enigma
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    Angle C = 60 degrees.

    Use:

    c^2=a^2+b^2-2ab\cos C

    7^2=a^2+8^2-2a(8)\cos 60

    49=a^2+64-8a

    a^2-8a+15=0

    Solve the quadratic.
    Last edited by mr fantastic; May 27th 2009 at 04:19 AM.
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