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Homework Help: Why they stack the vector that way

  1. Feb 17, 2009 #1
    v1 is
    (0)
    (1)
    (2)
    (3)

    v2 is
    (2)
    (a)
    (1)
    (0)

    W1 is
    (3)
    (1)
    (1)
    (0)

    W2 is
    (-2)
    (4)
    (2)
    (6)

    i am asked to find the dim of v+w ??

    i was told to flip each vector by 90 degrees
    so
    (a)
    (b)
    (c)
    (d)

    in the matrix presented a a row (a b c d)
    and then do a row reduction

    but they just keep it as it they were originaly (as columns) and do a row reduction

    0 2 3 -2
    1 a 1 4
    2 1 1 2
    3 0 0 6


    ??
     
  2. jcsd
  3. Feb 17, 2009 #2

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    Hi transgalactic! :wink:

    I'm not sure what your question is,

    but if you're asking whether using a column reduction is just as valid as using a row reduction, the answer is yes. :smile:
     
  4. Feb 17, 2009 #3
    no they present them as columns instead of flipping them
    and then they do a row reduction

    ??
     
  5. Feb 17, 2009 #4

    HallsofIvy

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    Science Advisor

    He answered your question: it doesn't matter whether you represent vectors as columns or rows!
     
  6. Feb 18, 2009 #5
    ahhh ok
    thanks :)
     
  7. Feb 20, 2009 #6
    it does matter
    because when i flipped it and did a row reduction i got
    -2 4 2 6
    0 10 8 6
    0 0 -2-8a -6a+36
    0 0 0 10a+40

    but in the not flipped version i get
    1 0 0 -2
    0 1 0 4
    0 0 1 2
    0 0 0 -3a -3

    ??
     
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