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Math Help - Please Help with problem with matrices, reflections, rotations

  1. #1
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    Please Help with problem with matrices, reflections, rotations

    Looking for help with a problem I'm working on:

    "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.

    Can anyone help me with this?

    thanks,
    Della
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  2. #2
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    Joined
    Oct 2009
    Posts
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    2
    Quote Originally Posted by dellatorre View Post
    Looking for help with a problem I'm working on:

    "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.

    Can anyone help me with this?

    thanks,
    Della

    You did the hardest part...way to go! Now just realize that you get the original matrix if you multiply the second (on the left) and third one (on the right...in this order!)...this is what "show that..." means!

    Tonio
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  3. #3
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    Dec 2009
    Posts
    3
    thank you
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