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Galois Conjugate


A Galois conjugate of an algebraic element alpha over a field F is an element sigma(alpha), where sigma is a field embedding of F(alpha) into an algebraic closure of F that fixes every element of F. The operation of replacing an algebraic element by one of its Galois conjugates is sometimes called Galois conjugation.

When the minimal polynomial of alpha over F is separable, the Galois conjugates of alpha over F are precisely the distinct roots of this minimal polynomial in an algebraic closure of F. In particular, if K/F is a Galois extension and alpha in K, then the Galois conjugates of alpha in K are the elements in the group orbit {sigma(alpha):sigma in Gal(K/F)}.

For example, the Galois conjugate of sqrt(5) over Q is -sqrt(5), and the Galois conjugate of the golden ratio phi=(1+sqrt(5))/2 over Q is

 phi^'=(1-sqrt(5))/2=1-phi=-1/phi.

Similarly, if zeta_n is a primitive nth root of unity, then its Galois conjugates over Q are the roots zeta_n^k with gcd(k,n)=1.


See also

Algebraic Conjugate, Conjugate Elements, Field Automorphism, Galois Group, Galois Theory, Minimal Polynomial

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References

Artin, E. Galois Theory, 2nd ed. Notre Dame, IN: Edwards Brothers, 1944.Dummit, D. S. and Foote, R. M. "Galois Theory." Ch. 14 in Abstract Algebra, 3rd ed. Hoboken, NJ: Wiley, pp. 558-654, 2004.

Cite this as:

Weisstein, Eric W. "Galois Conjugate." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/GaloisConjugate.html

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