Question 149567
3 1 2
3 2 -1
1 1 1
---------------
http://www.hostsrv.com/webmab/app1/MSP/quickmath/02/pageGenerate?site=mathcom&s1=matrices&s2=inverse&s3=basic
--------------
There's info and a tutorial there.
----------
The inverse times 7 is:
3  1  -5
-4 1   9
1 -2   3

*** all divided by 7.