Proving (ab)^n=e: A Group Theory Question | Homework Statement

In summary, the conversation discusses how to prove that if a and b are in a group and (ab)^n=e, then (ba)^n=e. The conversation involves using the property of associativity and 'cancellation' to show that (ba)(ba)(ba)=(ba). The conversation also suggests playing around with the equations abab=e and ababab=e to come up with a general argument for all n, and potentially using induction on n.
  • #1
eddyski3
8
0

Homework Statement



If a and b are in a group, show that if (ab)^n=e then (ba)^n=e.

Homework Equations





The Attempt at a Solution



I'm not sure how one would prove this. The question is obviously for non-abelian groups.
 
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  • #2
If (ab)^2=e then (ab)(ab)=e. So b(ab)(ab)a=bea=ba. Now use associativity and 'cancellation'. Do you see how to do the same trick for (ab)^n?
 
  • #3
I'm not sure how this helps us show that (ba)^2=e? When generalizing to (ab)^n I see we'll get a similar result but I'm not sure how this shows that (ba)^n=e.
 
  • #4
b(ab)(ab)a=ba, yes? That's the same as (ba)(ba)(ba)=(ba). Do you see it now?
 
  • #5
abab=e , so ab=b-1a-1

ababab=e , so baba=a-1b-1

Play around with these until you can figure out one, then , if you don't have a general
argument for all n, maybe induction on n will help.
 
  • #6
Oh, ok. Now I understand the argument. Thank you.
 

1. What is group theory?

Group theory is a branch of mathematics that studies the properties and structures of groups, which are mathematical objects that consist of a set of elements and a binary operation. It is widely used in various fields of science, including physics, chemistry, and computer science.

2. What does it mean to prove (ab)^n=e?

To prove (ab)^n=e means to show that raising the product of two elements, a and b, in a group to the power of n results in the identity element, e. This is a fundamental concept in group theory and is known as the exponent rule.

3. Why is proving (ab)^n=e important?

Proving (ab)^n=e is important because it helps establish the structure and properties of a group. It also allows us to understand how the elements in a group interact with each other and how they can be manipulated to produce different elements.

4. What are some techniques used to prove (ab)^n=e?

There are various techniques that can be used to prove (ab)^n=e, including direct proof, proof by contradiction, and proof by induction. These techniques involve using the properties and axioms of groups, such as closure, associativity, and the existence of an identity element.

5. Can (ab)^n=e be proven for any group?

No, (ab)^n=e cannot be proven for any group. It is only valid for groups that satisfy certain conditions, such as being finite, having a binary operation that is associative, and containing an identity element. Moreover, the value of n may differ for different groups.

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