Congruency and Divisibility of Odd in Z

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Homework Help Overview

The problem involves proving that 1 is the only common divisor of an odd integer n and n+2. The discussion centers around the properties of divisibility and congruence in relation to odd integers.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the relationship between the integers n and n+2, questioning the implications of common divisors and congruences. Some express confusion about the connection between the congruence and the divisibility conditions.

Discussion Status

Participants are actively engaging with the problem, with some providing insights into the nature of divisors and the implications of n being odd. There is a recognition that d must be either 1 or 2, but confusion remains regarding how to proceed with the proof.

Contextual Notes

There is an emphasis on the properties of odd integers and the implications for divisibility, with participants questioning whether an even divisor can apply to an odd integer.

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Homework Statement


Let n be any odd integer. Prove that 1 is the only "common" divisor of the integers n and n+2.

The Attempt at a Solution


I don't think I understand the question.

The few notes I have state d| (n+2 )- n

This resembles n+2 ##\equiv## n mod d , but I don't see the connection.
The congruency means that n+2 and n share the same remainder.
Any help?
 
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knowLittle said:

Homework Statement


Let n be any odd integer. Prove that 1 is the only "common" divisor of the integers n and n+2.

The Attempt at a Solution


I don't think I understand the question.

The few notes I have state d| (n+2 )- n

This resembles n+2 ##\equiv## n mod d , but I don't see the connection.
The congruency means that n+2 and n share the same remainder.
Any help?

The problem doesn't have anything to do with congruency. If d is a common divisor then d divides n and d divides n+2, so it follows that d must divide (n+2)-n. Don't you agree? Now use that to solve the problem.
 
Thank you. I agree.
I understand that
##d | n+2 -n ##

## n+2 -n = dq, ## where q ## \in Z##
Since, 2 = dq, so d and q could be 1 or 2.
 
knowLittle said:
Thank you. I agree.
I understand that
##d | n+2 -n ##

## n+2 -n = dq, ## where q ## \in Z##
Since, 2 = dq, so d and q could be 1 or 2.

Correct, that d must be 1 or 2. Now can you prove the original problem?
 
I thought that I already did.
d |n and d| n+2
n =dk and n+2 = dp, k and p are in Zn is odd, so n =2a+1 for some a in Z.

dk +2 =dp
2a+1 +2 = dp
2(a+1) + 1 = dp

I think this means that I am confused.
 
knowLittle said:
I thought that I already did.
d |n and d| n+2
n =dk and n+2 = dp, k and p are in Z


n is odd, so n =2a+1 for some a in Z.

dk +2 =dp
2a+1 +2 = dp
2(a+1) + 1 = dp

I think this means that I am confused.

Yeah, it does look like you have lost your way. It's much simpler than that. You know d=1 or 2. You are given that n is odd. d divides n. Can d be 2?
 
An even number can never divide an odd number. 'd' must be 1. :>

Thanks.
 

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