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Homework Help: Proving H is normal

  1. Oct 31, 2008 #1
    1. The problem statement, all variables and given/known data

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

    2. Relevant equations


    3. The attempt at a solution

    I cannot figure out what makes a subgroup H special if it is the only one of a given order...
  2. jcsd
  3. Oct 31, 2008 #2
    Pick a g in G. What is the order of g-1Hg?
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