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(a unit eigenvector)help!

  1. Dec 5, 2005 #1
    If A is a symmetric nxn mx of rank<=r>=1 and X is a unit eigenvector of A, with eigenvalue a not= 0, let B=A - aXX^T. Show that B is symmetric and that N(A) is a proper subspace of N(B). Conclude that rank B=<r-1.
    i could show X is in N(B) but not in N(A). Does anyone know how I can prove it in general? Then,I could prove N(A) is a proper subspace of N(B). Thanks!
  2. jcsd
  3. Dec 6, 2005 #2
    I figured it out already.
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