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Homework Statement
Classify the groups of order 12.
Homework Equations
None.
The Attempt at a Solution
The professor has worked this out up to a point. He proved a corollary that states:
"Let G be a group of order 12 whose 3-Sylow subgroups are not normal. Then G is isomorphic to A_4."
After the proof he states:
"Thus, the classification of groups of order 12 depends only on classifying the split extensions of Z_3 by groups of order 4."
OK, fine. So I know that split extensions are semidirect products, and that there are only 2 groups of order 4. So I need to compute the following:
[itex]D_4 \times_{\alpha} \mathbb{Z}_3[/itex]
[itex]\mathbb{Z}_4 \times_{\beta} \mathbb{Z}_3[/itex]
(sorry, don't know how to make the symbol for semidirect products)
Here's where the confusion begins. If I compare the semidirect products above with the definition of the same, then I see that I have to find the homomorphisms [itex]\alpha: \mathbb{Z}_3 \rightarrow Aut(D_4)[/itex] and [itex]\beta: \mathbb{Z}_3 \rightarrow Aut(\mathbb{Z}_4)[/itex].
The second one isn't so bad, but I would really like to turn the first one around so that the homomorphism comes out of [itex]D_4[/itex]. That's because I've already done a homework exercise that gives me all of the homomorphisms out of [itex]D_{2n}[/itex].
So, first question: Is [itex]D_4 \times_{\alpha} \mathbb{Z}_3[/itex] for some [itex]\alpha[/itex] isomorphic to [itex]\mathbb{Z}_3 \times_{\gamma} D_4[/itex] for some [itex]\gamma[/itex]? In other words, can I arrange it so that I'm looking for homomorphisms from [itex]D_4[/itex] to [itex]Aut(\mathbb{Z}_3)[/itex]?
Hope the question is clear.
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