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Use 3-digit arithmetic with no pivoting?

  1. Jul 24, 2014 #1
    1. The problem statement, all variables and given/known data
    Use 3-digit arithmetic with no pivoting to solve the following system:

    10-3x-y=1,
    x+y=0.


    2. Relevant equations
    I know that 10-3=0.001.


    3. The attempt at a solution
    The answer for this problem is (0, -1).
    Here's the work:
    1.001 0
    1 1

    I've set the augmented matrix and tried using the Gauss-Jordan method to solve the system but I got x=1/1.001 and y=-1/1.001, of course that's not the answer. How do I do this problem?
     
  2. jcsd
  3. Jul 24, 2014 #2
    Using Gauss-Jordian method, the matrix you should start off with is

    \begin{pmatrix} 10^{-3} & -1 & 1 \\ 1 & 1 & 0 \end{pmatrix}
     
  4. Jul 24, 2014 #3
    Thank you. Don't answer this question anymore. I've already solved it. Thanks again, everyone.
     
  5. Jul 25, 2014 #4

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    I wouldn't bother with matrices. Subtracting .001x+ y= 0 from x+ y= 1, y is eliminated, and we have .999x= 1. Divide both sides by .999, stopping at three decimal places.
     
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