1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Matrix ?

  1. Mar 30, 2008 #1
    solve eqautions using a matrix

    x + y -z = 0
    3x - y + z = 4
    5x +z = 7

    so i wrote the matrix

    1 1 -1 0
    3 -1 1 4
    5 0 1 7

    then i multiplied Row 1 by -3 and added that to row 2
    and multiplied row 1 by -5 and added that to row 3
    resulting in

    1 1 -1 0
    0 -4 4 4
    0 -5 6 7

    then i multiplied row 2 by - 1/4

    1 1 -1 0
    0 1 -1 -1
    0 -5 6 7

    then multiplied row 2 by 5 and added that to row 3

    1 1 -1 0
    0 1 -1 -1
    0 0 1 2

    now i subbed back in to eqns

    x + y -z = 0
    3x - y + z = 4
    5x +z = 7

    1x + 1y - 1z = 0
    0x +1y - 1z = -1
    0x + 0y + 1z = 2

    so z = 2 and solving all the other equation i get x = 1 and y = 1
    is this right because i tried solving these by subtraction and got somthing different
     
    Last edited: Mar 30, 2008
  2. jcsd
  3. Mar 30, 2008 #2

    neu

    User Avatar

    You have not constructed a matrix equation, you have just rewritten the coefficients in some kind of array/pattern

    THe matrix equation is :

    [tex]\begin{pmatrix}
    1 & 1 & -1\\
    3&-1 & 1\\
    5&0&1
    \end{pmatrix}
    \begin{pmatrix}
    x\\
    y\\
    z
    \end{pmatrix}
    =
    \begin{pmatrix}
    0\\
    4\\
    7
    \end{pmatrix}

    [/tex]
     
    Last edited: Mar 30, 2008
  4. Mar 30, 2008 #3
    The augmented matrix that 2slow to go fast used is correct.
    All you need to do is plug x y and z back into your original equations and see if they make true statements.
    Looks to me like they check out.
    CC
     
  5. Mar 30, 2008 #4
  6. Mar 30, 2008 #5
    i just got it i was substituting wrong thanks for the help
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Matrix ?
  1. What matrix is this? (Replies: 2)

  2. Matrix question (Replies: 7)

  3. Matrix Problem (Replies: 5)

Loading...