Conjugacy Classes and Group Order

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SUMMARY

The number of elements in a conjugacy class of a finite group divides the order of the group, as established by the orbit-stabilizer theorem and the class equation. Specifically, when a finite group G acts on itself via conjugation, the relationship |G| = |Orb(x)||Stab(x)| holds true. This demonstrates that the size of each conjugacy class is equal to the index of the centralizer of any representative element, confirming that the size divides the group's order.

PREREQUISITES
  • Understanding of finite groups and group order
  • Familiarity with Lagrange's Theorem
  • Knowledge of the orbit-stabilizer theorem
  • Basic concepts of conjugacy classes in group theory
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  • Explore Lagrange's Theorem and its applications in group theory
  • Learn about the class equation and its implications
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This discussion is beneficial for students and educators in abstract algebra, particularly those studying group theory, as well as mathematicians interested in the properties of finite groups and their conjugacy classes.

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Homework Statement


Is there a proof that the number of elements in a conjugacy class of a group has to divide the order of the group?
Everyone seems to cite it left and right but I've not seen a proof of it anywhere.


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The Attempt at a Solution


I'm guessing Langrange's Theorem may come into play but since conjugacy classes themselves aren't subgroups I'm not sure how.
 
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It is a trivial* consequence of the orbit-stabilizer theorem, or the class equation if you want to be fancy.

If G is a finite group acting on a set X, then |G|=|Orb(x)||Stab(x)|. Let X be G, and let the action be conjugation.

* Trivial in the sense of an immediate and obvious corollary, not something that is unimportant and easy.
 

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