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Homework Help: Help with math Matrices problem

  1. Sep 18, 2007 #1
    1. The problem statement, all variables and given/known data
    Find the reduced row echelon form of the following matrix:

    \begin{array}{c}\ \\ \\ \end{array}\;\begin{vmatrix}\;-4 & 0 & 4\;\\\;2 & -4 & 1\\\;-4 & 4 & -2\end{vmatrix}

    3. The attempt at a solution
    \begin{array}{c}\ \\ \\ \end{array}\;\begin{vmatrix}\;1 & 0 & 1\;\\\;0 & 1 & \frac{1}{4}\\\;0 & 0 & 1\end{vmatrix}

    I've tried it a few times and keep getting that answer. I've inputted that answer and it's wrong. Am I supposed to keep reducing the third row (even though those are constants?)
  2. jcsd
  3. Sep 18, 2007 #2
    Look at your last row. It says 0x+0y=1 (Assuming this is an augmented matrix)
  4. Sep 19, 2007 #3
    I figured it out. I was supposed to make the 1 and 1/4 in the third row zero's as well.
  5. Sep 19, 2007 #4


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    Science Advisor

    Yes, what you showed was "row echelon" form. "Reduced row echelon reduces above the diagonal also. Actually, untill you get down to a row all 0s you will have just the identity matrix.
  6. Sep 19, 2007 #5
    I had assumed not to touch the last row because that is usually the row of constants. In this case it wasn't - I had just assumed it was. :cool:
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