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PLEASE HELP! How to Cross Product Two 3x3 matrices

  1. Dec 3, 2009 #1
    How do I take the cross product of Two 3x3 Matrices.

    For example what is cross product of:
    [-1 0 0]
    [0 1 0]
    [0 0 1]
    x
    [0 -1 0]
    [1 0 0]
    [0 0 1]

    thanks,
    Della
     
  2. jcsd
  3. Dec 3, 2009 #2

    Hurkyl

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    The cross product isn't an operation on matrices -- your question doesn't make sense as given. Can you provide more information?
     
  4. Dec 3, 2009 #3
    ok, maybe its not the cross product I need to do then.

    The problem I'm struggling with is this:
    "Show that matrix
    [0 -1 0]
    [-1 0 0]
    [0 0 1]
    for a reflection about line y=-x
    is equivalent to a reflection relative to the y axis followed by a counter-clockwise rotation of 90 degrees."

    So for my answer, first I have for the reflection relative to the y axis, I have the matrix:
    [-1 0 0]
    [0 1 0]
    [0 0 1]

    and for the counter-clockwise rotation of 90 degrees, I have the matrix:
    [0 -1 0]
    [1 0 0]
    [0 0 1]

    but then I don't know what my next step should be.

    Do you know how to do this?

    thanks,
    Della
     
  5. Dec 4, 2009 #4
  6. Dec 4, 2009 #5

    Fredrik

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    That one changes the x coordinate of the vector it acts on, not the y coordinate.

    Multiply the matrices.
     
    Last edited: Dec 4, 2009
  7. Dec 4, 2009 #6
    thank you all :-))
     
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