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Math Help - Vectors

  1. #1
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    Vectors

    In the quadrilateral, ABCD, AB = r, BC = s, CD = t and DA = u

    which of the following statements is true?

    A.) r+s = t+ u
    B.) r + s = t - u
    C.) r - s = t - u
    D.) r + s = -t - u
    E.) r - s = u - t

    my answer was A, but the book says its D

    another question when subtracting vectors, do you just change the arrowhead of the negative vector of do you move the entire arrow to face the other direction?


    2.) If m = 3i - 2j and n = i + j

    a.) show that 2m + 4n is parallel to the x-axis

    i know how to do the substitution bit, but how do i show that it is parallel

    thanks alot guys
    Last edited by andrew2322; May 25th 2008 at 04:25 AM.
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    Hello,

    Quote Originally Posted by andrew2322 View Post
    In the quadrilateral, ABCD, AB = r, BC = s, CD = t and DA = u

    which of the following statements is true?

    A.) r+s = t+ u
    B.) r + s = t - u
    C.) r - s = t - u
    D.) r + s = -t - u
    E.) r - s = u - t

    my answer was A, but the book says its D
    \vec{r}+\vec{s}=\vec{AC}

    But \vec{t}+\vec{u}=\vec{CA} !

    Draw a picture

    another question when subtracting vectors, do you just change the arrowhead of the negative vector of do you move the entire arrow to face the other direction?
    I don't understand ?

    I think... :
    If you want to draw a vector substracted to another, draw a line parallel to the vector, starting at the endpoint of the vector to which you are going to substract, but going the opposit direction.


    2.) If m = 3i - 2j and n = i + j

    a.) show that 2m + 4n is parallel to the x-axis

    i know how to do the substitution bit, but how do i show that it is parallel

    thanks alot guys
    The x axis is defined by \vec{i}.
    That is to say that a vector \vec{v} is parallel to the x axis if and only if there exists k, such that \vec{v}=k \vec{i}

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