Groups whose elements have order 2

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Homework Help Overview

The discussion revolves around a group theory problem where the original poster is tasked with demonstrating that a group \( G \) in which every non-identity element has order two is commutative. The context involves properties of group elements and their orders.

Discussion Character

  • Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the implications of elements having order two and attempt to show that two elements commute using algebraic manipulation. Questions arise about the validity of the approach and the desire for alternative methods of proof.

Discussion Status

The discussion has seen some agreement on the initial approach, with participants affirming the correctness of the reasoning presented. However, there is also a desire for additional methods to demonstrate the same result, indicating an ongoing exploration of the topic.

Contextual Notes

Participants note that the order two aspect of the problem is distinct from a subsequent question regarding generators of \( \mathbb{Z}_n \) and their relationship to relative primality, suggesting a separation of the two topics in their discussions.

halvizo1031
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Homework Statement



suppose that G is a group in which every non-identity element has order two. Show that G is commutative.

Homework Equations





The Attempt at a Solution


Is my answer correct?

Suppose that a,b and ab all have order two. we will show that a and b commute. By assumption, e=(ab)^2
=abab
As a and b are their own inverses, multiplying on the left by a and then b,
we get
ba=ab.
 
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Looks good to me.
e = abab implies
b = ababb = aba which implies
ba = abaa = ab
 
Yes, that's right.
 
VeeEight said:
Looks good to me.
e = abab implies
b = ababb = aba which implies
ba = abaa = ab

Thanks! Is there another way i can show this?
 
halvizo1031 said:
Thanks! Is there another way i can show this?

Why do you need another way? What did you have in mind?
 
Dick said:
Why do you need another way? What did you have in mind?

well i just don't want to have the same answer as someone else.
 
halvizo1031 said:
well i just don't want to have the same answer as someone else.

It's a simple problem. There's a simple answer. There's a few different permutations on the expression of that answer, but they are all really the same. Wouldn't it be better to move on to the next problem?
 
Dick said:
It's a simple problem. There's a simple answer. There's a few different permutations on the expression of that answer, but they are all really the same. Wouldn't it be better to move on to the next problem?

That's true. I'm having trouble showing that an element k is a generator of Zn if and only if k and n are relatively prime.
 
halvizo1031 said:
That's true. I'm having trouble showing that an element k is a generator of Zn if and only if k and n are relatively prime.

The order 2 part of the problem has nothing to do with proving k is a generator of Zn if k and n are relatively prime. Try thinking about them independently.
 
  • #10
Dick said:
The order 2 part of the problem has nothing to do with proving k is a generator of Zn if k and n are relatively prime. Try thinking about them independently.

Sorry, i forgot to mention that this question has nothing to do with the order 2 problem. Here's the new question:

Consider 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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