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Math Help - basic vectors help

  1. #1
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    basic vectors help

    basic vectors help-c4.jpg

    Hi there,

    I'm stuck on the above question (part b). The part i'm actually stuck on is adding vector components (I think this is what it's called)

    ABCD is a rectangle. I have the coordinates of A (4, -2, 3), B (2, 0, -1) and C (5.5, 5.5, 0).

    To find D i'm told by the markscheme that OD = OA + BC. What does this actually mean?

    I don't have anything like this in the book i've been studying from so i've no idea how to complete the question.

    Thank you for any help
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  2. #2
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    Re: basic vectors help

    Quote Originally Posted by disintegration View Post
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    ABCD is a rectangle. I have the coordinates of A (4, -2, 3), B (2, 0, -1) and C (5.5, 5.5, 0).

    To find D i'm told by the markscheme that OD = OA + BC. What does this actually mean?
    You can find D=C+(A-B).
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  3. #3
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    Re: basic vectors help

    What I would do is this: find the equation of the plane, containing B, perpendicular to the vector AB. Determine where the line l crosses that plane. That will be the point "C". After that, it should be easy.
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    Re: basic vectors help

    Quote Originally Posted by Plato View Post
    You can find D=C+(A-B).
    This is the thing, I don't understand these basics or why that will give the coordinates of D. Is there anywhere I can learn this stuff?
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  5. #5
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    Re: basic vectors help

    Quote Originally Posted by disintegration View Post
    This is the thing, I don't understand these basics or why that will give the coordinates of D. Is there anywhere I can learn this stuff?
    It is basic geometry. Opposite sides of a rectangle are parallel and have the same length.
    In case of vectors this means \overrightarrow {BA}  = \overrightarrow {CD}.
    A-B gives us \overrightarrow {BA} this we get D by C+(B-A).
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