Galois and Klein 4: Isomorphic or Cyclic?

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SUMMARY

The discussion centers on the Galois group Gal(F/G) of a polynomial g(x) in G[x], where F splits over G and has no irreducible factors with repeated roots. Given that the degree of the field extension [F:G] is 4, the Galois group must be either isomorphic to the Klein four-group or a cyclic group of order 4. The key question posed is how to determine which structure the Galois group possesses, specifically by identifying a permutation of order 4 that would indicate a cyclic group.

PREREQUISITES
  • Understanding of Galois theory and field extensions
  • Familiarity with group theory, specifically Klein four-group and cyclic groups
  • Knowledge of polynomial roots and their permutations
  • Experience with the concept of irreducibility in polynomials
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  • Study the properties of Galois groups, focusing on the Klein four-group and cyclic groups
  • Learn how to compute permutations of polynomial roots to identify group structures
  • Explore examples of field extensions of degree 4 and their Galois groups
  • Investigate the implications of repeated roots in polynomial factorization
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Mathematicians, particularly those specializing in algebra and Galois theory, as well as students seeking to deepen their understanding of group structures in relation to polynomial equations.

morganjp
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suppose a +ve degree polynomial g(x) in G[x] with F splits over G and no irr. factor has repeated root. then if [F:G]=4, we know the size of Gal(F/G) is also 4. so it's either isomorphic to the Klein 4 or cyclic group of order 4. is there any trick to tell it's one and not the other?
 
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The Galois group will permute the roots. Can you find a permutation of order 4?
 

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