Matrices on the TI-89

Test Preparation
1

<p>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. </p>

<p>Any idea ??</p>

2

<p>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.</p>

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

<p>[[1,2,3][4,5,6][7,8,9]]</p>

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

<p>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:</p>

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

<p>OR</p>

<p>det([[1,2,3][4,5,6][7,8,9]])</p>

3

<p>Also, if you want to make matrices without typing in all of the individual brackets, you can do the following:</p>

<p>2nd–>Math–>Matrix–>newMat(</p>

<p>and then type in the dimensions: newMat(rows, columns)</p>

<p>You get a matrix of all 0’s, which you can then replace rather quickly with anything at all.</p>

4

<p>Thanks!</p>

<p>However, is there any way to compute 4X4 matrices with variables instead of numbers??</p>

5

<p>You can compute determinants of matrices with variables by just putting variables in, e.g. det([[w, x][y, z]]).</p>

6

<p>But it doesn’t seem to work with variables with 3X3 or 4X4 determinants.</p>

7

<p>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.</p>

8

<p>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.</p>

9

<p>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.</p>

<p>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.</p>

<p>Cheers</p>

10

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!