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Homework Help: Examining an augmented matrix

  1. Sep 24, 2012 #1
    I attached the problem.

    I just wanted to check if I'm thinking about a few of these parts correctly.

    a) yes because the coefficient matrix has 2 rows that are multiples of each other, thus det=0
    b)Yes, but the system does not have a unique solution b/c 2 rows are multiples of each other in the coefficient matrix.
    c) Imma skip this
    d) skipping this
    e) I think they worded this problem wrong. if det(coefficient matrix)=0, then there exists either inifinite many solutions OR NO solutions.
    f) skip

    Attached Files:

  2. jcsd
  3. Sep 25, 2012 #2


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    Consider what happens if, say, a = 1 and d = 1.
    And whether there are infinitely many solutions or no solutions depends on a, b, c, d. I agree that the wording of this question is strange.
  4. Sep 25, 2012 #3


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    It is unfortunate that you skipped over c and d because they are essential to e and f! d asked you to tell what must be true of the last column in order that the system be "inconsistent". e asks you to tell wheter or not, in that case, there are an infinite number of solutions or no solution. What does "inconsistent" mean?

    f happens to give you a set of values in which the last number is twice the first number. Do you see why that is important?
  5. Sep 25, 2012 #4
    Well since 2 rows in the coefficient matrix are multiples of each other, the system is either going to have a free variable, thus one option is infinite solutions. But if it's inconsistent, then there's no solutions. I don't think it's possible for the system to have a unique solution independent of a, b, c, d.

    Well I did them, posting my work would have just taken a while.
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