Centralizer Math Help: Proving <a> is a Subset of C(a) for Abelian Groups

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Homework Help Overview

The discussion revolves around proving that the cyclic subgroup generated by an element \( a \) is a subset of the centralizer \( C(a) \) in the context of abelian groups. Participants are exploring the implications of the commutativity condition \( xa = ax \) and its relation to the structure of the group.

Discussion Character

  • Conceptual clarification, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the definition of the cyclic subgroup generated by \( a \) and its relationship to the centralizer. There are attempts to clarify the implications of \( xa = ax \) and whether it leads to conclusions about the nature of \( C(a) \). Some participants express confusion about how to demonstrate that elements of the cyclic subgroup commute with \( a \).

Discussion Status

The discussion is ongoing, with various interpretations of the definitions and properties of the groups being explored. Some participants have offered clarifications about the nature of \( C(a) \) and the cyclic subgroup, while others are still grappling with the implications of their reasoning.

Contextual Notes

There is a mention of the potential confusion arising from the notation used for group operations, as well as the distinction between commutative and non-commutative groups. Participants are also considering the implications of whether \( a \) is in the center of the group.

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Homework Statement


Show <a>[tex]\subseteq[/tex]C(a) where C(a) is such that xa=ax.



Homework Equations





The Attempt at a Solution


Knowing xa=ax tells me we have an abelian group.
 
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Also a is in G
 


<a> is a cyclic subgroup
 


we have x=a^n . Need to show x=a^n is a subset of xa=ax. Not sure how to do that
 


So x=aaaaaaaaaa
a^-1x=a^n-1
I have no clue where my thought process has gone wrong, but it's really frustrating me
 


You have to show that for every [itex]n[/itex], [itex]a^n[/itex] commutes with [itex]a[/itex]. There's almost nothing to prove.
 


kathrynag said:

Homework Statement


Show <a>[tex]\subseteq[/tex]C(a) where C(a) is such that xa=ax.



Homework Equations





The Attempt at a Solution


Knowing xa=ax tells me we have an abelian group.
No, it doesn't. It tells you that C(a) is the set of all members of G that commute with a. If G is commutative, then C(a)= G. Otherwise C(a) is a subset of G.

Now, exactly what is the definition of <a>. Yes, I know it is the cyclic subgroup generated by a, but exactly what is that? Note that it is common to use either "multiplicative" notation, ab, or "additive" notation, a+ b, for the group operation. How would <a> be written in those two notations?
 


HallsofIvy said:
No, it doesn't. It tells you that C(a) is the set of all members of G that commute with a. If G is commutative, then C(a)= G. Otherwise C(a) is a subset of G.
If you meant "proper subset", you have to further assume that a is not in the center of G.
 

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