Maximal Ideals - Exercise 5.1 (iii) Rotman AMA

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Discussion Overview

The discussion revolves around Exercise 5.1, Part (iii) from Joseph J. Rotman's "Advanced Modern Algebra," specifically focusing on maximal ideals in the context of polynomial rings over fields. Participants explore the properties of these ideals, their generation by irreducible polynomials, and the implications of the Fundamental Theorem of Algebra.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Peter seeks assistance in starting Exercise 5.1, Part (iii) and expresses uncertainty about the problem.
  • Some participants propose that in a field $F$, the ring $F[x]$ is a Euclidean domain, which implies it is a principal ideal domain and a unique factorization domain, leading to maximal ideals being generated by irreducible polynomials.
  • It is noted that irreducible polynomials are also prime ideals, creating a connection between the two concepts.
  • One participant suggests that due to the Fundamental Theorem of Algebra, Part (iii) may be simpler than Part (ii), although this claim is met with some confusion regarding the similarities between the two parts.
  • Another participant points out that $\Bbb C[x]$ has a different variety of irreducible polynomials compared to $\Bbb R[x]$, citing the example of $x^2 + 1$ being reducible in $\Bbb C[x]$ but irreducible in $\Bbb R[x]$, attributing this difference to the algebraic properties of the fields.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the Fundamental Theorem of Algebra for the exercise, and there is no consensus on the clarity of the relationship between Parts (ii) and (iii) of the exercise. Additionally, the discussion highlights a disagreement regarding the nature of irreducible polynomials in different fields.

Contextual Notes

The discussion reflects varying interpretations of the properties of polynomial rings over different fields and the implications for maximal and prime ideals. There are unresolved questions regarding the relationship between parts of the exercise and the specific characteristics of irreducible polynomials in $\Bbb C[x]$ versus $\Bbb R[x]$.

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I am reading Joseph J. Rotman's book: Advanced Modern Algebra (AMA) and I am currently focused on Section 5.1 Prime Ideals and Maximal Ideals ...

I need some help with Exercise 5.1, Part (iii) ... ...Exercise 5.1 reads as follows:
View attachment 5943Can someone please help me to get a start on this exercise ...

Peter
 
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Hint:

over a field $F$, the ring $F[x]$ is a Euclidean domain (with Euclidean function $\text{deg}$), and thus a fortiori a principal ideal domain, and also a unique factorization domain.

So maximal ideals are generated by irreducible polynomials, which *are* the prime ideals as well, since irreducibles are prime and vice-versa.

Due to the Fundamental Theorem of Algebra, part (iii) is actually easier than part (ii).
 
Deveno said:
Hint:

over a field $F$, the ring $F[x]$ is a Euclidean domain (with Euclidean function $\text{deg}$), and thus a fortiori a principal ideal domain, and also a unique factorization domain.

So maximal ideals are generated by irreducible polynomials, which *are* the prime ideals as well, since irreducibles are prime and vice-versa.

Due to the Fundamental Theorem of Algebra, part (iii) is actually easier than part (ii).
Thanks for the help, Deveno ... appreciate it

Not quite sure what you are saying about Part (ii) though ... again we have a PID and so again, as you say, the maximal ideals are generated by irreducible polynomials, which *are* the prime ideals as well, since irreducibles are prime and vice-versa ... so answer seems the same ...

Can you clarify ...

Peter
 
$\Bbb C[x]$ has a lesser variety of irreducible polynomials that $\Bbb R[x]$ does. For example, $x^2 + 1 = (x + i)(x - i)$ is reducible in $\Bbb C[x]$, but is irreducible in $\Bbb R[x]$.

This is because $\Bbb C$ is algebraically closed, and $\Bbb R$ is not.
 

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