How to find inverse of matrix?

Hi

Is there any special setting that I need to have on since I am getting the wrong inverse for one of my questions.

This is my original martix

17 17 5

21 18 21

2 2 19

this should be the inverse

4 9 15

15 17 6

24 0 17

I am getting on my calc(stopped after 3rd decimal place but there is like 10 or more decimal places)

-.319 .333 -.284

.380 -.333 .268

-.006 1.249 .054

So that is totally different

I put in my matrix by going 2nd-matrix-edit

then to inverse I did [A] then x-1 to get the -1 on top of it.

I have the ti-83 plus calc.