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Determinant of 4 x 4

  1. Jun 26, 2008 #1
    Ok, I have gotten different answers by reducing to an upper triangle, co-factor, and my calculator. All 3 giving me different answers!

    |Upper-triangle| = lol, was looking at the wrong problem ... I did get 36.
    |Co-factor reduction mobob| = uh i keep messing it up
    |Calculator| = 36

    1 2 3 0
    2 6 6 1
    -1 0 0 3
    0 2 0 7

    Expanding using row 3

    (a)
    -1
    2 3 0
    6 6 1
    2 0 7

    (b)
    -3
    1 2 3
    2 6 6
    0 2 0

    Expanding once again to reduce it to a 2 x 2

    (a)
    -1 times determinant of these 2 x 2

    2
    3 0
    6 1

    7
    2 3
    6 6

    (b)
    -3

    -2
    1 3
    2 6
     
    Last edited: Jun 26, 2008
  2. jcsd
  3. Jun 26, 2008 #2

    Dick

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    Maxima, the free computer software of my choice, says 36. Doing it by hand the determinant of your first 3x3 is -36. The determinant of the second 3x3 is 0.
     
    Last edited: Jun 26, 2008
  4. Jun 26, 2008 #3
    Ok the book answer has to be wrong then.
     
  5. Jun 26, 2008 #4

    Dick

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    I really think it is 36.
     
  6. Jun 26, 2008 #5

    HallsofIvy

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    "Row reduction" reduces that matrix to
    [tex]\left[\begin{array}{cccc}1 & 2 & 3 & 0 \\0 & 2 & 0 & 1 \\ 0 & 0 & 3 & 2 \\ 0 & 0 & 0 & 6[/tex]
    and the product along the diagonal is 36.
     
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