- #1

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## Homework Statement

Here's the problem I don't understand and its solution:

http://img11.imageshack.us/img11/5867/24545624.gif [Broken]

## Homework Equations

## The Attempt at a Solution

I want to write the original matrix as a product of elementary matrices but I don't know they got that set of 4 elementary matrices. Can anyone help me to see how to get those elementary matrices?

I can row reduce the original matrix to rref but I don't see how that helps. (Actually the matrix when in reduced row echelon form is the identity, indicating that it is invertible.)

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