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Homework Help: Linear Algebra (Find A^43)

  1. Oct 28, 2012 #1
    *new question, playing with projection matrix.

    Well I have a new question about the A(ATA)-1AT matrix.

    http://puu.sh/1jXT6 [Broken]

    I was able to show that BT was idempotent, but my manipulation was a bit different from the teacher for B2

    Let B2 = (A(ATA)-1AT)(A(ATA)-1AT)

    I did (AA-1(AT)-1AT)A(ATA)-1AT = IA(ATA)-1AT=A(ATA)-1AT=B

    The teacher did it in another method and I don't think my method is correct because it doesn't make sense that B = I.
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Oct 28, 2012 #2


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    Hi Lifprasir! :smile:

    (try using the X2 button just above the Reply box :wink:)
    Because S3(u) = u, S3(v) = v :wink:
  4. Oct 28, 2012 #3
    Ooooooooooooooooooooh. Thank you so much!!!
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