Proving Normality in Group Theory: Guide and Tips for Proving H is Normal in G

In summary, to prove that H is normal in G when N is a cyclic normal subgroup of G and H is a subgroup of N, we can use the fact that conjugation does not change the order of elements in a cyclic group. Additionally, in an abelian group G, the set G(n) consisting of elements with order n is a subgroup of G. This holds true for all subgroups of a cyclic group, meaning that all subgroups of G are of the form G(n).
  • #1
moont14263
40
0
Please can someone help me to prove this
If N is a cyclic normal subgroup of G and H is a subgroup of N then H is normal in G.
 
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  • #2
You'll need to use the following:

If x in N has order k, then gxg-1 also has order n.

So conjugation won't change the order of the elements, and order of the elements determine which subgroup the element will belong to (in cyclic groups).
 
  • #3
Could you give me more hints because I am not that much in cyclic groups. Thank you.
 
  • #4
Show that, if G is abelian and if n is a number, then [tex]G(n)=\{g\in G~\vert~g^n=e\}[/tex] is a subgroup of G.

Then show that, if G is cyclic, then all subgroups of G are of the form G(n).
 

Related to Proving Normality in Group Theory: Guide and Tips for Proving H is Normal in G

What is group theory?

Group theory is a branch of mathematics that deals with the study of groups, which are mathematical structures that consist of a set of elements and a binary operation that combines two elements to produce a third element that belongs to the same set.

What are the applications of group theory?

Group theory has many applications in various fields such as chemistry, physics, cryptography, and computer science. It is used to study the symmetries and patterns in physical systems, to understand the behavior of molecules and atoms, and to design secure encryption algorithms.

What is a group in group theory?

A group in group theory is a set of elements that is closed under a binary operation and satisfies four axioms: closure, associativity, identity, and inverse. The binary operation must also be commutative for the group to be considered abelian.

What are the basic concepts in group theory?

Some of the basic concepts in group theory include subgroups, cosets, normal subgroups, quotient groups, and group homomorphisms. These concepts are used to understand the structure and properties of groups and to prove theorems in group theory.

What are some useful theorems in group theory?

Some of the most useful theorems in group theory include Lagrange's theorem, which states that the order of a subgroup must divide the order of the group, and the first isomorphism theorem, which relates the structure of a quotient group to the structure of the original group.

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