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Unformatted text preview: n Corollary 7.5.3. Aut K .E/ acts faithfully by permutations on the roots of f.x/ in E . The action is transitive on the roots of each irreducible factor of f.x/ . Proof. By Exercise 7.4.5 , Aut K .E/ acts faithfully by permutations on the roots of f.x/ and, by the previous corollary, this action is transitive on the roots of each irreducible factor. n Theorem 7.5.4. Suppose that K C is a eld, f.x/ 2 Kx , and E is the splitting eld of f.x/ in C . Then Fix . Aut K .E// D K . Sketch of proof. We have a priori that K Fix . Aut K .E// . We must show that if a 2 L n K , then there is an automorphism of E that leaves K xed pointwise but does not x a . n Corollary 7.5.5. If K M E is any intermediate eld, then Fix . Aut M .E// D M ....
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 Fall '08
 EVERAGE
 Algebra, Factor Theorem

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