# 0 divisors and solutions in ax=b

1. Nov 5, 2007

### Glass

1. The problem statement, all variables and given/known data
Prove that if a is a 0 divisor of some ring, then for any b of the ring, ax=b cannot have one x that satisfies the equation (i.e. cannot have one solution)

2. Relevant equations

3. The attempt at a solution
It seems to me this isn't even right. Say a is a right 0 divisor but not a left. Then ax=0 has only one solution (namely x=0) so unless all right 0 divisors are left 0 divisors (which I didn't think is true) isnt' this a contradiction of the theorem I'm trying to prove?

2. Nov 6, 2007

### morphism

It's telling you that a is a 0 divisor, i.e. both a right and left 0 divisor.

3. Nov 7, 2007

### matt grime

Firstly, morphism is correct, but I wanted to add this: you say

"Say a is a right 0 divisor but not a left. Then ax=0 has only one solution (namely x=0)"

This means that a right 0 divisor means a *is not* a left 0 divisor. Be careful of saying things like that. The status of a as a right 0 divisor means nothing about it as a left 0 divisor (unless the ring is abelian under *).