You can put this solution on YOUR website! 3 1 2
3 2 -1
1 1 1
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http://www.hostsrv.com/webmab/app1/MSP/quickmath/02/pageGenerate?site=mathcom&s1=matrices&s2=inverse&s3=basic
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There's info and a tutorial there.
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The inverse times 7 is:
3 1 -5
-4 1 9
1 -2 3
*** all divided by 7.