F_2(α) isomorphic to F_2[x]/<f(x)>

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Homework Help Overview

The discussion revolves around proving that the field extension \(\mathbb{F}_2(\alpha)\) is isomorphic to the quotient ring \(\mathbb{F}_2[x]/\), where \(f(x)\) is a polynomial in \(\mathbb{F}_2[x]\) that has a root \(\alpha\) in an extension field \(E\) of \(\mathbb{F}_2\). Participants are exploring the implications of this isomorphism in the context of field theory.

Discussion Character

  • Conceptual clarification, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the application of the first isomorphism theorem and the need to demonstrate surjectivity and identify the kernel of the mapping from \(\mathbb{F}_2[X]\) to \(\mathbb{F}_2[\alpha]\). There is also a question regarding the equivalence of \(\mathbb{F}_2[\alpha]\) and \(\mathbb{F}_2(\alpha)\).

Discussion Status

The discussion is active, with participants raising questions about the validity of certain assumptions and the correctness of the proof approach. Some guidance has been offered regarding the first isomorphism theorem, but there is no explicit consensus on the correctness of the initial proof setup.

Contextual Notes

One participant points out a potential issue with the choice of polynomial \(f(X)=(X-1)^2\), suggesting that it does not yield a field, which raises questions about the assumptions underlying the proof.

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Homework Statement


Show that [tex]\mathbb{F}_2(\alpha)[/tex] is isomorphic to [tex]\mathbb{F}_2[x]/ <f(x)>[/tex].

where [tex]f(x)\in\mathcal{F}_2[x][/tex] and [tex]E\supseteq\mathcal{F}_2[/tex] is an extension of [tex]\mathbb{F}_2[/tex] such that [tex]f(x)[/tex] has a root [tex]\alpha\in E[/tex]. Also [tex]\mathbb{F}_2(\alpha)[/tex] is the subfield [tex]E[/tex] generated by [tex]\mathbb{F}_2[/tex] and [tex]\alpha[/tex].

Homework Equations


The Attempt at a Solution


Could anyone give me some direction on how to start this proof?
 
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What about the first isomorphism theorem?

Show that [tex]\mathbb{F}_2[X]\rightarrow \mathbb{F}_2[\alpha][/tex] is a surjection and find it's kernel...
 
micromass said:
What about the first isomorphism theorem?

Show that [tex]\mathbb{F}_2[X]\rightarrow \mathbb{F}_2[\alpha][/tex] is a surjection and find it's kernel...

is it ok to say [tex]\mathbb{F}_2[\alpha]=\mathbb{F}_2(\alpha)[/tex]?
 
rukawakaede said:
is it ok to say [tex]\mathbb{F}_2[\alpha]=\mathbb{F}_2(\alpha)[/tex]?

I'm sorry, I missed that. But now that you mention it, it seems that it is not correct what you're trying to prove: Take f(X)=(X-1)2. Then F[X]/(X-1)2 is not a field and can thus not be isomorphic to a field.
 

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