Proving Normalcy of H in Finite Group G

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SUMMARY

If G is a finite group with exactly one subgroup H of a given order, then H is normal in G. This conclusion follows from the properties of cosets, where the left cosets and right cosets of H in G coincide. The proof relies on the definition of normal subgroups and the unique existence of H, leading to the conclusion that for any element x in G, the conjugate xHx-1 equals H.

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joecoz88
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I have been struggling with this proof:

If G is a finite group with exactly one subgroup H of a given order, then H is normal.

I'm not sure where to start...
 
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What can you say about xHx-1 for any x in G?

You only need to write down the definitions and it becomes obvious
 
What can you say about the left and right cosets of H in G? Do they coincide under those conditions?

Once you can establish that, it is trivial.
 

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