Are Normal Subgroups Defined by Equality of Left and Right Cosets?

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In summary, normal subgroups are subgroups that are closed under conjugation by all elements of the group and have the property that left cosets and right cosets are the same, allowing for the creation of a separate group of cosets.
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raj123
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Normal subgroups??

Normal subgroups?
 
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H is normal if gHg^(-1)=H for all g. If H is a subgroup of some order, then so is gHg^(-1). End of hint.
 
  • #3
Ah so

If H is unique subgroup of order n (no others) it must be normal as all other xHx^(-1) must be of that same order n.

I was thrown by the 10 or 20 in the problem, but it could really be any order n.

Thank you very much for the hint. I saw the disclaimer after I posted about the homework, so I'm sorry if this question wasn't up to par.
 
  • #4
Also, a subgroup, H, of a group, G, is a normal subgroup if and only if the "left cosets" and "right cosets" are the same. A result of that is that we can define the group operation on the cosets (if p is in coset A and q is in coset B then AB is the coset that contains pq) in such away that the collection of cosets is a group in its own right: G/H.
 

What is a normal subgroup?

A normal subgroup is a subset of a group that is closed under the group operation and also satisfies a certain condition called normality. This condition means that the normal subgroup is invariant under conjugation by elements of the larger group.

How is a normal subgroup different from a subgroup?

A normal subgroup is a special type of subgroup that has the property of normality, while a subgroup does not necessarily have this property. This means that a normal subgroup is preserved under conjugation by elements of the larger group, whereas a subgroup may not be.

What is the significance of normal subgroups?

Normal subgroups are important in the study of groups because they allow us to define quotient groups, which are groups formed by taking the larger group and "modding out" the normal subgroup. This allows us to study the structure of the original group in a simpler way.

How can I determine if a subgroup is normal?

There are a few ways to determine if a subgroup is normal. One way is to check if every element of the subgroup is invariant under conjugation by elements of the larger group. Another way is to see if the subgroup is the kernel of a homomorphism from the larger group to another group.

Can a group have more than one normal subgroup?

Yes, a group can have multiple normal subgroups. In fact, the trivial subgroup (containing only the identity element) and the entire group itself are always normal subgroups of any group. It is also possible for a group to have only one normal subgroup or no normal subgroups at all.

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