http://i453.photobucket.com/albums/q...188/math10.jpg

Help would be appreciated.

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- November 19th 2008, 12:50 PMpkrCommutative Ring
http://i453.photobucket.com/albums/q...188/math10.jpg

Help would be appreciated. - November 19th 2008, 06:41 PMThePerfectHacker
We will first prove that if then is a unit. This is simple, . Thus, are inverses of eachother. Say that is a unit. Since it means and so since the ring is commutative. Using the above result it means is a unit. But then is a unit.

- November 20th 2008, 04:51 AMpkr
So for the 2X2 Matirx would you take B to be the matrix (0 1, 0 0) as that squared = (0 0, 0 0)

This is confusing me slightly, I haven't seen the notation of a "unit" in this context before...What exactly would the conditions be I need to satisfy for A-B to not be a unit? - November 20th 2008, 12:39 PMThePerfectHacker
- November 20th 2008, 12:51 PMpkr
Many thanks, all sorted now!