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# Matrices on the TI-89

edited April 2013
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

• Registered User Posts: 336 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)
• Registered User Posts: 52 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.
• Administrator Posts: 32,337 Senior Member
Thanks!

However, is there any way to compute 4X4 matrices with variables instead of numbers??
• Registered User Posts: 2,142 Senior Member
You can compute determinants of matrices with variables by just putting variables in, e.g. det(w, x][y, z).
• Administrator Posts: 32,337 Senior Member
But it doesn't seem to work with variables with 3X3 or 4X4 determinants.
• Registered User Posts: 336 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.
• Administrator Posts: 32,337 Senior 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.
• Registered User Posts: 1 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
• Registered User Posts: 1 New Member
I registered on this site just to thank you for this! I couldn't figure out why I was unable to do symbolic matrix algebra for the longest time. Turns out I had to clear the values. Thanks!
This discussion has been closed.