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Order of ab?

  1. Oct 21, 2009 #1
    Suppose G is a group, a,b are two elements of G, does o(ab)=lcm(o(a),o(b))?
    o(ab) denotes the order of ab, lcm(o(a),o(b)) denotes the Least Common Multiple of o(a) & o(b).
  2. jcsd
  3. Oct 21, 2009 #2


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    It is true when a and b commute, and can easily be proven in that case.
    When a and b do not commute, the statement is false. For a counterexample, you could try to find some elements in S3 (e.g. there are elements a and b such that o(a) = 2, o(b) = 3, o(a, b) = 2).
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