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Homework Help: Sum of additive(?) groups

  1. Oct 26, 2012 #1
    Z is the set of integers. Prove that (3/7)Z + (11/2)Z = (1/14)Z


    By definition,
    (3/7)Z+(11/2)Z={3k/7 + 11m/2 : k,m € Z} = {(6k + 77m)/14 : k,m € Z}.

    Showing that 3/7Z+11/2Z is a subset of 1/14 Z is easy but I can't prove the converse. Can't show that whatever n€1/14Z I take satisfies that n€3/7Z+11/2Z.
  2. jcsd
  3. Oct 26, 2012 #2


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    If you could show 1/14 is in the group 3/7Z+11/2Z, then all multiples of 1/14 would also be in the group, right?
  4. Oct 26, 2012 #3
    Yes! If I take k=13 and m=-1 then 1/14 is in the group 3/7Z+11/2Z. Thank you very much.
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