Which elements of z42 are invertibles?

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Homework Help Overview

The discussion revolves around identifying the invertible elements in the group of integers modulo 42, denoted as z42. Participants explore the concept of invertibility in relation to the elements being relatively prime to the order of the group.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Some participants attempt to list the elements they believe are invertible based on their notes, questioning whether the property of being relatively prime applies universally to all groups. Others raise inquiries about the nature of inverses and whether there can be multiple elements that are their own inverses.

Discussion Status

The discussion is active, with participants sharing their thoughts and questioning the generality of the concept of invertibility. A hint referencing Fermat's little theorem has been introduced, suggesting a deeper exploration of the reasoning behind the relationship between invertibility and relative primality.

Contextual Notes

Participants are considering the implications of their findings in the context of group theory, specifically regarding the properties of invertible elements and their relationship to the group's order. There is an ongoing exploration of assumptions related to the definitions and characteristics of groups.

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Homework Statement



which elements of z42 are invertibles?

Homework Equations





The Attempt at a Solution



In my notes I have that invertibles are relatively prime to the order of the group. So I have

1, 5, 11, 13, 17, 19, 23, 25, 29, 31, 37, 41.

Is that the case for all groups?
 
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duki said:

Homework Statement



which elements of z42 are invertibles?

Homework Equations





The Attempt at a Solution



In my notes I have that invertibles are relatively prime to the order of the group. So I have

1, 5, 11, 13, 17, 19, 23, 25, 29, 31, 37, 41.

Is that the case for all groups?

Is what the case for all groups?

Interesting fact: Note that 1 is its own inverse. That leaves 11 invertibles, so if you repeatedly remove pairs of invertibles, you have at least one left without a partner, meaning it has to be its own inverse. Which one is it? Is there an easy way to spot it? Is there more than one?
 


Is what the case for all groups?
Can you always take the relatively primes and get the invertibles?
 


duki said:
Can you always take the relatively primes and get the invertibles?

Yes, but do you know why? Hint: can you apply Fermat's little theorem?
 

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