Simple Matrices Multiplication Question

[Narmer]

I have a matrix:

1 2 1
0 1 0
-1 -3 -1

If you square that, the book says that the answer is:

0 5 0
0 1 0
0 -8 0

But I think the answer should be:

0 1 0
0 1 0
0 -2 0

I'm sure that for any nxn matrix, you multiply the row of the left matrix by the column by the right matrix, where they intersect is where the sum goes.

 

[JetBlack69]

Just glancing at it, I think you are right.

 

[desteffy]

you look correct to me too

 

[Narmer]

Thanks guys, I was really afraid of that. I'm also curious as to what other mistakes have been made in this book.

BTW, this is a Differential Equations book. I'm currently on the chapter about Linear Differential Equations. What really bothers me in this chapter is that they make a very important proposition contingent on the fact that AB=BA, where A and B are matrices. That's a rarity in Linear Algebra so how can they base their important propositions on such a rare occurance? Are Diff. Eq. really that difficult to solve? I plan on bringing this up with my professor on Tuesday.