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Homework Help: Computing the order of a group

  1. Sep 6, 2007 #1
    1. The problem statement, all variables and given/known data

    Let a be an element of a group an let |a| = 15. Compute the orders of the following elements of G

    a) a^3, a^6, a^9, a^12

    2. Relevant equations

    3. The attempt at a solution

    for the first part of part a, would a^3 be <a^3>=<e,a^3,a^6,a^9,a^12,a^15,a^18,a^21,a^24,a^27,a^30, a^33,a^36,a^39,a^42>
  2. jcsd
  3. Sep 6, 2007 #2


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    |a|=15 means that 15 is the lowest power of a that is equal to the identity.

    So, for example,
    [tex]a^{42}=a^{15}\times a^{15} \times a^{12}=e \times e \times a^{12}=a^{12}[/tex]
    so you've got too many things in your list.
  4. Sep 6, 2007 #3

    matt grime

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    What I want to know is why the OP stopped after a^42 in particular. I mean going beyond a^15 is clearly wrong, but why stop at a^42? Is that the 15th power of a^3? I think so, from quickly scanning the list.
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