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 04-20-2005, 11:36 PM #1 _AroW_ Guest   Posts: n/a Matrices on the TI-89 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 ?? Reply
 04-20-2005, 11:44 PM #2 Member   Join Date: Apr 2005 Posts: 332 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( -> -> ) OR det([[1,2,3][4,5,6][7,8,9]]) Reply
 04-20-2005, 11:58 PM #3 Junior Member   Join Date: Apr 2005 Location: Bay Area Posts: 52 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. Reply
 04-21-2005, 12:45 PM #4 _AroW_ Guest   Posts: n/a Thanks! However, is there any way to compute 4X4 matrices with variables instead of numbers?? Reply
 04-21-2005, 02:42 PM #5 Senior Member   Join Date: Aug 2004 Location: CA Posts: 2,120 You can compute determinants of matrices with variables by just putting variables in, e.g. det([[w, x][y, z]]). Reply
 04-22-2005, 11:28 PM #6 _AroW_ Guest   Posts: n/a But it doesn't seem to work with variables with 3X3 or 4X4 determinants. Reply
 04-23-2005, 12:54 AM #7 Member   Join Date: Apr 2005 Posts: 332 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. Reply
 04-23-2005, 01:12 PM #8 _AroW_ Guest   Posts: n/a 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. Reply
 04-14-2013, 06:50 PM #9 New Member   Join Date: Apr 2013 Posts: 1 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 Reply

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