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Math Help - Inverse Matrix help!

  1. #1
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    Red face Inverse Matrix help!

    Can someone explain how you do inverse matrices with a 2X2 and 3X3 matrix? Please.
    Here are two problems and I don't know how to get the answers.

    R1 is -1 -2
    R2 is 3 4

    the 3X3 is
    R1 is 1 0 1
    R2 2 1 3
    R3 -1 1 1

    TIA!
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  2. #2
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    assuming you know how to transpose a matrix and fin the determinant:

    inverse of 2x2 matrix is 1/determinant[matrix transposed]



    3x3 matrix is 1/determinant[adjugate matrix]
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  3. #3
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    Quote Originally Posted by djmccabie View Post
    assuming you know how to transpose a matrix and fin the determinant:

    inverse of 2x2 matrix is 1/determinant[matrix transposed]



    3x3 matrix is 1/determinant[adjugate matrix]
    Hi, I don't think that is correct. My book says that A is NOT = to 1/A because A is a matrix and not a number
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  4. #4
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    The answer for the first one is (its in the back of the book and I don't know how to do it.)

    R1 is 2 1
    R2 -1.5 -.5
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  5. #5
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    Quote Originally Posted by scottydoint View Post
    Can someone explain how you do inverse matrices with a 2X2 and 3X3 matrix? Please.
    Here are two problems and I don't know how to get the answers.

    R1 is -1 -2
    R2 is 3 4

    the 3X3 is
    R1 is 1 0 1
    R2 2 1 3
    R3 -1 1 1

    TIA!

    2x2 matrix
    detA = (top left)(bottom right)-(top right)(bottom left)
    detA = -4 - (-6)
    detA = 2

    matrix transposed = 4 -3
    2 -1

    so inverse = 1/2[4 -3]
    [2 -1]

    do you need the 3x3 matrix explained?
    Last edited by djmccabie; November 24th 2008 at 03:34 PM. Reason: did it wrong!!
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  6. #6
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    arghhh now times what i just did by the original matrix! lol im useless
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  7. #7
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    ok, I kinda get it now. can you do the 3X3 please.
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  8. #8
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    does it work? i dont seem to get the answer in the book? its gettin late in the uk lol.

    3x3 matrix

    first find the determinant.

    R1 is 1 0 1
    R2 2 1 3
    R3 -1 1 1

    this is 1(1-3)-0(-3-2)+1(2--1)
    =-2-0+3
    =1

    Now find all the minor determinants of each element.

    R1 -2 0 3
    R2 -1 2 1
    R3 -1 1 1

    then add a minus sign to each of the even numbered elements.

    R1 -2 -0 3
    R2 +1 2 -1
    R3 -1 -1 1

    Transpose the matrix


    R1 -2 1 -1
    R2 0 2 -1
    R3 3 -1 1

    now multiply by the 1/determinant found at the beginning

    1 * New Matrix


    hope this helps,


    more importantly i hope this is right lol
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