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Matrices on the TI-89

CC ArticlesCC Articles Posts: 1- New Member
How do I use the TI-89 to find the determinants of 3X3 and 4X4 matrices? I only know how to do 2X2, but that would be a waste of time since I can cross multiply.


Any idea ??
Post edited by Unknown User on

Replies to: Matrices on the TI-89

  • ShaheinShahein Posts: 336Registered User Member
    Well... If you download the Equation Writer program it becomes a lot easier... However, this is a way to input matrices using the calculator alone.

    The format is
    (the bracket key is located on the comma key (2nd comma) which is immediately left of division):

    [[1,2,3][4,5,6][7,8,9]]

    This produces a 3x3 like this:
    |1 2 3|
    |4 5 6|
    |7 8 9|

    Then you can use the standard matrix operator functions under 2nd Math to find the determinant. For the previous matrix, the determinant would be typed in as follows:

    2nd -> Math -> det( -> <matrix> -> )

    OR

    det([[1,2,3][4,5,6][7,8,9]])
  • Archon496Archon496 Posts: 52Registered User Junior Member
    Also, if you want to make matrices without typing in all of the individual brackets, you can do the following:

    2nd-->Math-->Matrix-->newMat(

    and then type in the dimensions: newMat(rows, columns)

    You get a matrix of all 0's, which you can then replace rather quickly with anything at all.
  • CC ArticlesCC Articles Posts: 1- New Member
    Thanks!

    However, is there any way to compute 4X4 matrices with variables instead of numbers??
  • im_blueim_blue Posts: 2,142Registered User Senior Member
    You can compute determinants of matrices with variables by just putting variables in, e.g. det([[w, x][y, z]]).
  • CC ArticlesCC Articles Posts: 1- New Member
    But it doesn't seem to work with variables with 3X3 or 4X4 determinants.
  • ShaheinShahein Posts: 336Registered User Member
    what kind of variable entry are you talking about here? The 89 doesn't seem to do very will with multi-variable stuff (unless you have some programs: implicit differentiation requires a program and some other stuff). Post an example please.
  • CC ArticlesCC Articles Posts: 1- New Member
    I mean instead of numbers in the determinant I put in viariables such as a , b, c instead. For 3x3 or 4x4 it says error: non algebvraic variable in expression.
  • FutureReferenceFutureReference Posts: 1Registered User New Member
    Hi, just registered because I found the solution to this problem. Hopefully it'll help for those people that search for the same problem and have arrived at this thread.

    If you get "error: non algebraic variable in expression" that means you have something stored in one of your variables. To fix this, press 2nd, f1, 1, enter.

    Cheers
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