$3\times3$ matrix inverse and multiplication

Question

Which answer is correct? Mine or this from the textbook?

There is an easy way to check -- compute $AB$ and you should get the diagonal matrix with diagonal $1,1,-1$ — gt6989b, Sep 23 '19 at 17:04

score 1 · Accepted Answer · answered Sep 23 '19 at 17:10

1

You can check that your answer multiplied by $B$ gives the correct matrix. The textbook is wrong.

answered Sep 23 '19 at 17:10

kccu

thanks, I probably wouldn't have known how to do that on wolframalpha otherwise. – Adam Rubinson Sep 23 '19 at 17:25
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@AdamRubinson Check it by hand. These aren’t very big matrices. – amd Sep 23 '19 at 18:18
Yeah so what? With this question, I was also checking I hadn't given the incorrect matrix for AB to begin with. And just because I can compute these by myself doesn't mean it's not useful to know I could use wolframalpha for bigger matrices or more complicated matrix multiplication – Adam Rubinson Sep 23 '19 at 20:48

1 Answers1