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Math Help - vector problem

  1. #1
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    Question vector problem

    Marie is training for the Marathon. From her home, she runs 5 km south west. She then changes direction and run 3 km N 20 W to get to the park.

    a) how far and what direction is the park from Marie's home?

    R^2 = 3^2 + 5^2 - 2 x 3x5 cos 65

    R^2 = 50.8

    R = 7.12

    In my textbook the R = 4.6. What am I doing wrong?
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  2. #2
    MHF Contributor
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    Re: vector problem

    Your calculator is set to compute the cosine of angles measured in radians instead of degrees. Indeed, 3^2 + 5^2 = 34, and cos 65 > 0, so 3^2 + 5^2 - 2 x 3x5 cos 65 cannot be 50.8.
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