Proof of abelian-ness if every element is also its own inverse


by Juanriq
Tags: abelianness, element, inverse, proof
Juanriq
Juanriq is offline
#1
Oct15-10, 10:15 AM
P: 42
Salutations! I just want to make sure I am on the right track...

1. The problem statement, all variables and given/known data

Let G be a group. Prove that if every element in a group is equal to its own inverse, then G is abelian

2. The attempt at a solution

Pick two elements [latex] a, b \in \thinspace G[/latex]. By assumption, [latex]a = a^{-1}[/latex] and [latex] b = b^{-1}[/latex]. Our goal is to show that [latex] ab = ba[/latex]. By our assumption, the following holds
[latex]
ab = a^{-1}b^{-1}
[/latex]
Since G is a group, it is closed under inverses, therefore we can take the inverse of both sides
[latex]
(ab)^{-1} = \bigl (a^{-1} b^{-1} \bigl )^{-1} = \bigl (b^{-1} \bigl )^{-1} \bigl (a^{-1} \bigl )^{-1} = ba
[/latex]

Thanks!
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deluks917
deluks917 is offline
#2
Oct15-10, 10:39 AM
P: 367
ab is an element of G, what does that mean (ab)^-1 is by assumption?
Juanriq
Juanriq is offline
#3
Oct15-10, 12:31 PM
P: 42
Oh! By assumption [latex] ab = (ab)^{-1} [\latex] as well. That definitely makes this a simple one-liner when I apply the inverse and initial assumpition to the right side. Thanks!


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