Proving C is the Smallest Constructible Numbers Subfield with a>0 Property

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SUMMARY

The field C of constructible numbers is established as the smallest subfield of R with the property that if a is in C and a > 0, then √a is also in C. The discussion emphasizes the necessity of demonstrating that any proper subfield C' of C cannot maintain this property if it excludes certain elements of C. The approach includes exploring techniques such as repeated squaring to validate that elements not in C' must still belong to C, thereby reinforcing C's status as the minimal subfield with the specified property.

PREREQUISITES
  • Understanding of constructible numbers in the context of field theory
  • Familiarity with the properties of subfields and their definitions
  • Knowledge of real numbers and their properties
  • Basic concepts of algebraic structures and operations
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  • Study the properties of subfields in field theory
  • Learn about constructible numbers and their geometric interpretations
  • Explore the concept of repeated squaring in algebra
  • Investigate the relationship between fields and their extensions
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Mathematicians, students of abstract algebra, and anyone interested in the foundational properties of fields and constructible numbers.

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Homework Statement



Show that the field C of constructible numbers is the smallest subfield of R with the property that [tex]a\in C, a>0 \Rightarrow \sqrt{a}\in C[/tex].

The Attempt at a Solution



Suppose there's a proper subfield of C' of C that has that property, then let [tex]a\in C-C'[/tex]. Somehow I must show that a is actually in C. Perhaps repeated squaring?
 
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Maybe a different tactic would be useful?

Let C' be the smallest subfield with that property. Can you prove C is a subfield of C', and that C has that property?
 

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