If p(x) is a polynomial of degree n in F[x] and if E is the splitting field of p(x) over F, then (E:F) is a divisor of n!

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- Apr 18th 2010, 07:28 PMapple2009divisor
If p(x) is a polynomial of degree n in F[x] and if E is the splitting field of p(x) over F, then (E:F) is a divisor of n!

- Apr 19th 2010, 01:16 AMaliceinwonderland
If the polynomial p(x) is separable or characteristic of F is 0, then it can be shown directly like this.

If E is the splitting field of p(x) in F[x], then E is the Galois extension of F. Thus |Gal(E/F)| = [E:F]. Since Gal(E/F) is the subgroup of S_n (link), [E:F] should be a divisor of n! by Lagrange's theorem. - Apr 19th 2010, 07:33 AMNonCommAlg
prove it by induction over it's obvious for for consider two cases:

__case 1__: is irreducible. in this case for some and we have because is irreducible. also note that is a splitting

field for and thus, by induction hypothesis, divides therefore

__case 2__: is reducible. then for some with and we also have let be the splitting field for

which is contained in then would be a splitting field for thus, by induction hypothesis: