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Math Help - Trigonometry

  1. #1
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    Trigonometry

    Two sides of a paralellogram measure 7.0cm and 9.0cm. THe longer diagonal is 12 cm long. Calculate all the interior angles , to the nearest degree, of the paralellogram.
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  2. #2
    Member Henderson's Avatar
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    Do you know the Law of Cosines?

    c^2 = a^2 + b^2 - 2ab\cos(\theta), so
    12^2 = 7^2 + 9^2 - 2(7)(9)cos(\theta).

    Solve that for \theta, and you have one angle, and its opposite. The other two angles are supplements of that angle ( 180 - \theta).
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