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Homework Help: Find pivot columns

  1. Sep 6, 2011 #1
    1. The problem statement, all variables and given/known data

    So, I want to find the pivot columns to the matrix A:

    A=
    -1 1 -5 0 2
    3 0 6 1 -1
    2 -1 7 2 1
    2 -7 25 5 1

    and after that I want to solve Ax = b where b is (I kind of want to solve Ax = 0 as well, but let's skip that...):

    b=
    a+3
    2a
    -a-1
    -9a-5

    My thought was to solve everything at the same time, and I started doing that by gausselimination. The problem is that I've been stuck for a while with this:

    C=
    15 0 -15 0 0
    0 3 0 0 0
    0 0 -6 -1 0
    0 0 0 5 10

    and

    d=
    26a+7
    a+2
    2a
    2a+14

    The zero at row 2, column 3 is giving me a headache, and I don't know how to solve it at all. Is it possible I made a mistake while doing these row operations?

    I'm very thankful for any kind of advice!
     
  2. jcsd
  3. Sep 12, 2011 #2

    vela

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    Staff Emeritus
    Science Advisor
    Homework Helper
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    Why is that 0 a problem?

    By the way, I think you did make a mistake reducing the matrix somewhere. When I reduced it, there were no fractions in the result, but it looks like you'll end up with some.
     
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