Proof about identity element of a group

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Homework Help Overview

The discussion revolves around proving that an element \( a \) in a group \( G \) acts as the identity element under a certain operation, given that \( a * b = b \) for some element \( b \) in \( G \).

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the idea of assuming \( a \) is not the identity and attempting to derive a contradiction. There are discussions about using the inverse of \( b \) and how to incorporate it into the reasoning.

Discussion Status

Participants are actively engaging with hints and suggestions, such as considering the inverse of \( b \) and manipulating the equation. There is a collaborative effort to clarify the approach without reaching a definitive conclusion.

Contextual Notes

There is an implicit assumption that the properties of groups, such as the existence of inverses and the definition of the identity element, are understood but not explicitly stated in the posts.

hoopsmax25
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Homework Statement


If G is a group, a is in G, and a*b=b for some b in G (* is a certain operation), prove that a is the identity element of G


Homework Equations





The Attempt at a Solution


I feel like you should assume a is not the identity element and eventually show that a= the identity. but I am not sure how to show that.
 
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Hint: Think about using ##b^{-1}##.
 
I thought about using the inverse of b but I'm not sure how to plug it in?
 
You don't "plug it in". You could try *-ing things with it.
 
Could you do a*b*b-inverse=b*b-inverse? and go from there?
 

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