how and what is an encoding matrix?

my instructor lately likes to give us a question and have us figure it out unfortunately dont know how to program calculator (ti-83 plus) and i have no notes on how o answer this question:

using the encoding matrix [2 3 5]
[7 11 13]
[17 19 23], i have encrypted the following me-
ssage: [115 234 128 152 200]
[398 708 421 444 583]
[724 1326 737 876 1115]

1. figure out the decryption matrix
2. Decrypt the message
3. what was the message i encrypted?

(Headbang)my problem is this sholud i plug this in on the calculate or right it out? and even so how would i right it out on the calculator?

directing me to other sites, so i can do research would greatly help me out. thank you

Have you considered the inverse of the Encoding Matrix?

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Originally Posted by TKHunny

Have you considered the inverse of the Encoding Matrix?

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I'm sorry i have not, in fact i am kinda stumped on how i even would start to answer this question using that said calculate. sorry i did not get back to you i was working :-)

Okay, can you do it?

An "encoding matrix" is a matrix, M, such that, if you write a message, in numerical form, as "X", then the coded form is MX= Y. Of course, then so the "decoding matrix" is the matrix inverse of M.