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Math Help - Idempotent Matrix

  1. #1
    Jon77
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    Idempotent Matrix

    Hi, can anyone help me with the following question please:

    Show that X(X’X)-1X’y is in the column space of X for any m-vector y.

    Where matrix X is of size (mxn)

    I have already proved that X(X’X)-1X’ is idempotent and symmetric, however I can't quite do the part at the top.
    Help needed urgently please!

    Thanks in advance...
    Last edited by Jon77; February 3rd 2008 at 10:50 PM.
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