Showing that Every Ideal of R has the Form mR

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Homework Help Overview

The problem involves showing that every ideal of the ring R, specifically when R is the integers modulo n (Zn), can be expressed in the form mR for some integer m. The discussion revolves around properties of ideals and the application of the division algorithm.

Discussion Character

  • Exploratory, Conceptual clarification, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the relevance of previously established results about principal ideals and the use of GCDs. There are attempts to apply the division algorithm, with some expressing confusion about how to proceed. Questions arise about expressing sums of ideals and the implications of the smallest positive element in an ideal.

Discussion Status

The discussion is active, with participants offering hints and suggestions regarding the use of the division algorithm and the structure of ideals. Some participants are exploring different interpretations of the problem, and there is a collaborative effort to clarify concepts without reaching a definitive conclusion.

Contextual Notes

There is a mention of the need to express ideals in a specific form and the constraints of working within the framework of Zn. Participants are also navigating the implications of the smallest element in an ideal and how it relates to the overall structure of the ideal.

kimberu
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Homework Statement


If R = Zn, show that every ideal of R has the form mR for some integer m.


Homework Equations


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The Attempt at a Solution


Well, by a previous problem I showed mR is the principal ideal of the ring, but I don't know if that's relevant. I was given the hint to try to use GCDs somehow, but I really have no ideas.

thanks so much!
 
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Use the division algorithm.
 
VeeEight said:
Use the division algorithm.

You mean, say that n = qd + r, or for m?
Sorry, I'm totally lost on this problem.
 
Suppose you have an ideal of the form mR+nR. How can you express this as a principal ideal?
 
kimberu said:
You mean, say that n = qd + r, or for m?
Sorry, I'm totally lost on this problem.

Let a be the smallest positive element in your ideal I. If you have some element x in I, then x = aq + s for some s less then a.
 
TMM said:
Suppose you have an ideal of the form mR+nR. How can you express this as a principal ideal?

Would it be (m+n)R?
 
VeeEight said:
Let a be the smallest positive element in your ideal I. If you have some element x in I, then x = aq + s for some s less then a.
So from here...can I say that s must equal 0 and x = aq for all x, since otherwise it's a contradiction because a is the smallest element?
 
Yes. You can also reproduce this proof for other rings such as the Eisenstein integers and the Gaussian integers.
 
VeeEight said:
Yes.

Thank you so much for walking me through! :)
 
  • #10
No problem, cheers.
 

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