PlanetMath (more info)
 Math for the people, by the people. Sponsor PlanetMath
Encyclopedia | Requests | Forums | Docs | Wiki | Random | RSS  
Login
create new user
name:
pass:
forget your password?
Main Menu
Owner confidence rating: High Entry average rating: No information on entry rating
Kummer theory (Theorem)

The following theorem is usually referred to as Kummer theory.

Theorem 1 (Kummer Theory)   Let $n$ be a positive integer and let $K$ be a field of characteristic not dividing $n$ which contains the $n$ -th roots of unity. Then:
  1. The extension $K(\sqrt[n]{a})$ for $a\in K$ is a cyclic extension over $K$ of degree dividing $n$ .
  2. Any cyclic extension of degree $n$ over $K$ is of the form $K(\sqrt[n]{a})$ for some $a\in K$ .
Definition 1   Let $n$ be a positive integer and let $K$ be a field of characteristic not dividing $n$ which contains the $n$ -th roots of unity. An extension of $K$ of the form: $$K(\sqrt[n]{a_1},\sqrt[n]{a_2},\ldots,\sqrt[n]{a_k})$$ with $a_i \in K^\times$ is called a Kummer extension of $K$ . Notice that the Galois group of the extension is of exponent $n$ .




"Kummer theory" is owned by alozano.
(view preamble | get metadata)

View style:

See Also: abelian extension, cyclic extension, exponent

Also defines:  Kummer extension
Keywords:  Kummer, abelian extension

Attachments:
proof of Kummer theory (Proof) by rm50
Log in to rate this entry.
(view current ratings)

Cross-references: Galois group, degree, cyclic extension, extension, roots of unity, contains, characteristic, field, integer, positive, theory, theorem
There are 5 references to this entry.

This is version 2 of Kummer theory, born on 2005-02-22, modified 2005-02-22.
Object id is 6793, canonical name is KummerTheory.
Accessed 4404 times total.

Classification:
AMS MSC12F05 (Field theory and polynomials :: Field extensions :: Algebraic extensions)

Pending Errata and Addenda
None.
Discussion
Style: Expand: Order:
forum policy

No messages.

Interact
post | correct | update request | prove | add result | add corollary | add example | add (any)