# Question about Linear Congruences

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• Jun 17th 2011, 02:14 PM
VinceW
Question about Linear Congruences
I'm reading a chapter on linear congruences such as $ax \equiv b (mod m)$

What is confusing me is this sentence, "we may ask how many of the m congruence classes modulo m give solutions; this is exactly the same as asking how many incongruent solutions there are modulo m".

Why are the congruence classes that give solutions considered incongruent? It would seem to me that is the opposite: they should be congruent solutions.

The example: Find all solutions to $9x \equiv 12 (mod 15)$. A complete set of three incongruent solutions is given by x=8, x=13, x=3. I understand how to calculate those three values of x, I don't understand why they are calling these "incongruent solutions".
• Jun 17th 2011, 03:13 PM
abhishekkgp
Re: Question about Linear Congruences
Quote:

Originally Posted by VinceW
I'm reading a chapter on linear congruences such as $ax \equiv b (mod m)$

What is confusing me is this sentence, "we may ask how many of the m congruence classes modulo m give solutions; this is exactly the same as asking how many incongruent solutions there are modulo m".

Why are the congruence classes that give solutions considered incongruent? It would seem to me that is the opposite: they should be congruent solutions.

The example: Find all solutions to $9x \equiv 12 (mod 15)$. A complete set of three incongruent solutions is given by x=8, x=13, x=3. I understand how to calculate those three values of x, I don't understand why they are calling these "incongruent solutions".

these are called mutually incongruent solutions because $3 \not \equiv 8 \not \equiv 13 (mod \, 15)$
now find any other $x$ which satisfies the congruence, that $x$ will be congruent (mod15) to either 3 or 8 or 13.
• Jun 18th 2011, 11:10 AM
VinceW
Re: Question about Linear Congruences
Ahh... Now it makes perfect sense. I'm glad I asked. Thanks!