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Homework Help: Find all matrices

  1. Feb 7, 2005 #1
    I would appreciate if someone could help me with this one.

    Matrix A=[1 0 ; 1 1]
    I need to find all matrices that satisfy: AB=BA
    How can I find them?
    PLease help :cry:
  2. jcsd
  3. Feb 7, 2005 #2


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    Try writing
    [tex]B=\left(\begin{array}{cc}a & b \\ c&d \end{array}\right)[/tex]

    and check what the constraints on a,b,c and d are.
  4. Feb 7, 2005 #3
    did that. And put A(inverse)* [a b;c d] = C*A(inverse)
  5. Feb 7, 2005 #4


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    What does the inverse have to do with everything...?

  6. Feb 7, 2005 #5
    yea, just write out AB=BA using B=[a,b;c,d] and A=[1,0;1,1]
    and multiply out both sides.
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