What is the difference between a field a subfield

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Discussion Overview

The discussion revolves around the concept of fields and subfields in mathematics, specifically addressing the definitions and properties that distinguish them. Participants explore examples such as the rational numbers (Q), real numbers (R), and integers (Z), and engage in clarifying the criteria that determine whether a subset qualifies as a subfield.

Discussion Character

  • Conceptual clarification, Debate/contested, Homework-related

Main Points Raised

  • Some participants assert that a subfield of a field is any subset of the field that is itself a field with the same operations.
  • There is a question about why Q is considered a subfield of R while Z is not, with some participants expressing confusion over this distinction.
  • Participants inquire about the field axioms and whether Z qualifies as a field, suggesting that the inability to divide integers to yield another integer is a reason Z is not a field.
  • One participant emphasizes that Z is not a field, and therefore cannot be a subfield.

Areas of Agreement / Disagreement

Participants generally agree on the definition of a subfield but express differing views on the specific examples of Q and Z, leading to unresolved questions about the criteria for being a field.

Contextual Notes

Limitations include the lack of a detailed explanation of the field axioms and the specific properties that differentiate fields from subfields, which remain unresolved in the discussion.

student34
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For example, my notes say, "Q (rationals) is a subfield of R (reals). Z (integers) is not a subfield of R. Any subfield (together with the addition and multiplication) is again a field".

This just doesn't make any sense to me.

Oops, this was suppose to be in the homework section - sorry.
 
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That should say something like
"A subfield of a field is any subset of the field that is itself a field (with the same operations)."
What you have
"Any subfield (together with the addition and multiplication) is again a field".
Is true, but not very useful without context.
 
lurflurf said:
That should say something like
"A subfield of a field is any subset of the field that is itself a field (with the same operations)."
What you have
"Any subfield (together with the addition and multiplication) is again a field".
Is true, but not very useful without context.

I still don't understand why Q is a subfield of R, but Z isn't.
 
student34 said:
I still don't understand why Q is a subfield of R, but Z isn't.

Is Z a field?
What are the field axioms?
 
Number Nine said:
Is Z a field?
What are the field axioms?

Oh, is it not a field because division of 2 integers can produce a number that isn't an integer?
 
^Yes. A subset is a subfield if it is itself a field (with the same operations). Z is not a field, so it is not a subfield.
 
Thank-you everyone!
 

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