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Math Help - [SOLVED] Cosine rule 2

  1. #1
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    Angry [SOLVED] Cosine rule 2

    If you could help me in any way it would be great!!! I accidently typed the wrong question!(I sometimes wonder how I got into this maths class=])
    this is the right question:
    A boat travels 6.3km due north and then turns 17degrees towards the west and travels a further 7.2kms. How far is it from it's initial position?

    x^2=6.3^2+7.2^2-2(6.3)(7.2)cos17
    x^2=91.53-90.72Xcos17
    x^2=91.53-86.76
    x^2=4.77
    x=2.18


    any help would be great! Thank you for taking the time to help me with my trig h/w!!
    Last edited by mr fantastic; February 10th 2009 at 04:27 AM. Reason: Deleted language that could cause offence.
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  2. #2
    Newbie geld's Avatar
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    I think you should try this... ?!

    x^2=6.3^2+7.2^2-2(6.3)(7.2)cos(180\deg - 17\deg )
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  3. #3
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    Hello, xch3m_is_l0v3x!

    You didn't make a sketch, did you?


    A boat travels 6.3km due north . {\color{blue}AB = 6.3}
    and then turns 17 towards the west . {\color{blue}\angle NBC = 17^o}
    and travels a further 7.2kms. . {\color{blue}BC = 7.2}
    How far is it from it's initial position?
    Code:
        C *           N
           \\         :
            \ \ 7.2   :
             \  \     :
              \   \17:
               \    \ :
                \     * B
                 \    |
                  \   |
                   \  | 6.3
                    \ |
                     \|
                      * A

    Get it? . . . You should have used: \angle ABC = 163^o

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