Are Relatively Prime Elements Generators of Cyclic Groups?

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SUMMARY

The discussion focuses on proving that an element k is a generator of the cyclic group Zn if and only if k and n are relatively prime. The proof requires two parts: first, demonstrating that if k and n are relatively prime, then k generates Zn; second, showing that if k generates Zn, then k and n must be relatively coprime. The key insight is that the order of an element m in Zn is n divided by the greatest common divisor (gcd) of m and n, which leads to the conclusion that if m is a generator, then gcd(m, n) must equal 1.

PREREQUISITES
  • Understanding of cyclic groups and their properties
  • Knowledge of the concept of relative primality
  • Familiarity with the greatest common divisor (gcd)
  • Basic proof techniques, including proof by contradiction
NEXT STEPS
  • Study the properties of cyclic groups in abstract algebra
  • Learn about the Euclidean algorithm for calculating gcd
  • Explore proof techniques in mathematics, focusing on proof by contradiction
  • Investigate the structure of the group Zn and its generators
USEFUL FOR

Mathematics students, particularly those studying abstract algebra, educators teaching group theory, and anyone interested in the properties of cyclic groups and number theory.

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Homework Statement


Zn={0,1,...,n-1}. show that an element k is a generator of Zn if and only if k and n are relatively prime.


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The Attempt at a Solution


it makes sense but I am having a hard time proving this.
 
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So you need to do two parts:
1) If k and n are relatively prime, k generates Zn. What do you need to prove to show this?

2) If k generates Zn, then k and n are relatively coprime. This part is probably easier done by proof by contradiction
 
Office_Shredder said:
So you need to do two parts:
1) If k and n are relatively prime, k generates Zn. What do you need to prove to show this?

2) If k generates Zn, then k and n are relatively coprime. This part is probably easier done by proof by contradiction

well i understand i need to show both ways but to be honest, this is all i have:
==>if m is in {0,1,...,n-1} is a generator, its order is n. Also, its order must be n/(m,n). Thus, n=n/(m,n) which implies (m,n)=1.
<== if (m,n)=1 then the order of m is n/(m,n)=n/1=n.
therefore, m is a generator of Zn.
 

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