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Groups/cyclic groups

  1. Oct 17, 2009 #1
    I need help here: Suppose that G is a group in which every non-identity element has order two. Show that G is commutative.

    Also, Consider Zn = {0,1,....,n-1}
    a. show that an element k is a generator of Zn if and only if k and n are relatively prime.

    b. Is every subgroup of Zn cyclic? If so, give a proof. If not, provide an example.
  2. jcsd
  3. Oct 18, 2009 #2


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    What does it mean that G is commutative?
    What possible ways to prove commutativity do you know of?

    For the second one, I suggest starting with the "<==" implication (i.e. assume that k and n are relatively prime and show that k generates Zn.
  4. Oct 18, 2009 #3

    for the first one, we can show commutativity with a multiplication table. How else?

    for the second one, i want to start with ==> and say that the order of k is n/(m,n). but how can i show it?
  5. Oct 19, 2009 #4


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    OK let's take them one at a time.

    The definition of commutativity is that xy = yx for any two elements x and y.
    Can you explicitly show this in the case given?
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