Abstract algebra help

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- May 6th 2013, 08:45 PMjamiebogabstract algebra
Abstract algebra help

- May 7th 2013, 03:43 PMjohngRe: Aut(H) ≈ Inn(H). Show that G ≈ H x C(H) if H is normal in G.
Hi,

I assume you mean Inn(H) is the group of inner automorphisms of H and when you say Aut(H) Inn(H), you really mean Aut(H)=Inn(H) -- the inner automorphisms__are__automorphisms. Also from your conclusion, you left out the necessary assumption that Z(H) is trivial.

Assume H is a normal subgroup of G, Z(H) is trivial and Aut(H)=Inn(H). To show , it is sufficient to show H and C_{G}(H) are normal, and . Since the centralizer is a normal subgroup and Z(H)=<1>, the only thing to prove is :

Let . Then conjugation of elements of H by x is an automorphism of H. So there exists with for all . That is, for all h in H and so . Thus .