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-   -   Algebra 2 finding the determinant of a four by four matrices using ellimination. (https://www.askmehelpdesk.com/showthread.php?t=418931)

  • Nov 24, 2009, 08:55 AM
    aseperatepeace
    Algebra 2 finding the determinant of a four by four matrices using ellimination.
    How do you find the determinant of this four by four matrices by using ellimination?

    MY MATRICES:

    0 -2 3 -4
    -5 -6 7 -8
    9 -10 11 -12
    13 -14 -15 16

    P.S I know how to find the determinant of a three by three and a two by two easily using ellimination, but struggle with a four by four.

    THANK YOU FOR YOUR TIME!
  • Nov 26, 2009, 09:00 AM
    galactus

    It is tedious to do these things by hand. In my opinion, it has become rather anachronistic to do these manually when calculators will do them lickety-split. The important thing is knowing when to use a det. Let a calculator do the grunt work. One can use cofactors. Or, using row reduction methods, turn the matrix into a upper or lower triangular matrix and bring out common factors to multiply.

    I will tell you the determinant is -2128.

    There is something to shoot for if you want to give it a go.

    There are some det laws that are helpful to know.

    Here is an example of what I mean.



    Interchange first and second rows:



    Remove a common factor of 3 from the first row:



    -2 times first row added to third row:



    -10 times second row added to third row:



    Remove a common factor of -55 from the last row:




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