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Math Help - Adding vectors to find displacement

  1. #1
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    Adding vectors to find displacement

    So I got this two vectors and I have used the pytagoream theorem to. But I'm still kinda sketchy about the answer I get.

    46225+7225 = 53450
    sqrt 53450 = 231km

    Did I do it right?
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  2. #2
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    Quote Originally Posted by drkidd22 View Post
    So I got this two vectors and I have used the pytagoream theorem to. But I'm still kinda sketchy about the answer I get.

    46225+7225 = 53450
    sqrt 53450 = 231km

    Did I do it right?..........Unfortunately no
    You only can use the Pythagorean theorem if the vectors are perpendicular to each other.

    In your case the vectors include an angle of 135 and therefore you have to use the Cosine rule:

    d = \sqrt{85^2+215^2-2 \cdot 85 \cdot 215 \cdot \cos(135^\circ)}

    I've got d \approx 281.59\ km
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  3. #3
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    How did you find the angle. I don't seem to understand that part. But I do understand about the perpendicular stuff and the right triangle.
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