Cosets of Subgroups: Is Each Class a Group?

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SUMMARY

The discussion centers on the properties of cosets in relation to subgroups within finite groups. It is established that cosets of a subgroup H partition the group G into equivalence classes, but not every coset is a group. Specifically, the coset is a group if and only if the subgroup H is normal. The example provided, H = {0, 4, 8, 12} in Z_16, illustrates that the right coset with 1 does not form a group, emphasizing the necessity of normality for the quotient group of cosets to be a group.

PREREQUISITES
  • Understanding of group theory concepts, specifically subgroups and cosets.
  • Familiarity with normal subgroups and their properties.
  • Knowledge of finite groups and their structure.
  • Basic grasp of quotient groups and their formation.
NEXT STEPS
  • Study the properties of normal subgroups in detail.
  • Learn about the construction and significance of quotient groups.
  • Explore examples of finite groups and their subgroup structures.
  • Investigate the implications of coset representatives in group theory.
USEFUL FOR

This discussion is beneficial for students of abstract algebra, particularly those studying group theory, as well as educators and researchers looking to deepen their understanding of subgroup properties and coset behavior.

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Homework Statement


Let H be a subgroup of a finite group G. I understand that the cosets of H partition G into equivalence classes. Is it always true that each of these equivalence classes is a group?

EDIT: clearly is it not always true; let H ={0,4,8,12} in Z_16 and take the right coset with 1; so are there conditions that make it true?

Homework Equations


The Attempt at a Solution

 
Last edited:
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I think the cosets form a group iff the subgroup H is normal.

Edit: sorry I think I misread; are you asking if each coset forms a group or if the collection of cosets forms a group?
 
Last edited:
Only one coset can be a group. The one containing e. The quotient group (collection of cosets) can be a group as Mathdope alluded to.
 

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