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Homework Help: A matrix issue

  1. Jun 27, 2009 #1
    1. The problem statement, all variables and given/known data
    So I'm doing a systems of DEs question with undetermined coefficients. After comparing coefficients, I have this:

    where a&b are vectors (2D) and A is the coefficient matrix:
    [2 -1]
    [3 -2]

    I know that 'a' is (1,1)T. I need to find b.

    I tried rearranging it, but I don't know if that's right.

    So I found A-I:
    [1 -1]
    [3 -3]

    I was going to invert it and multiply by (0,1), but it's not invertible. What do I do?
  2. jcsd
  3. Jun 27, 2009 #2


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    Science Advisor
    Homework Helper

    Hi Melawrghk! :wink:
    Yes, that's fine! :smile:
    Give up! :biggrin:

    A - I is a projection onto the line x = y (because it sends (p,q) to (p-q,p-q)), so you can't have (A - I)b = (0,1).
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