1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Prime p divides order of group

  1. Aug 21, 2013 #1
    1. The problem statement, all variables and given/known data.
    Let p be a prime number, m a natural number and G a group of order p^m. Prove that there exists an element a in G such that ord(a)=p.

    3. The attempt at a solution.
    I know of the existence of Lagrange theorem, so what I thought was: I pick an arbitrary element a (I exclude e, the identity element) of G and look at the group generated by that element, denoted as <a>. I also know that the order of <a> is equal to the order of the element a. Now I can apply Lagrange theorem: as the order of <a> divides the order of G, then the order of <a> must be of the form p^k for some natural number k, k≤m. I got stuck here, I can't deduce k=1 with only these statements, there is something missing.
     
  2. jcsd
  3. Aug 21, 2013 #2
    So if a has order p^k then which power of a has order p?
     
  4. Aug 21, 2013 #3

    verty

    User Avatar
    Homework Helper

    If the cyclic group generated by an element is always a subgroup, and if the order of that subgroup always divides the order of the group, then the claim will go through if there is always an element of order > 1. But on two sites I found, much more complicated proofs are given, induction on k with separate handling of the abelian/non-abelian cases. It could just be that they are written so as not to use Lagrange's Theorem.
     
  5. Aug 21, 2013 #4
    I got it, but just in case I want to check: Is it p^(k-1)?, because then (a^p^(k-1))^p=a^(pp^(k-1))=a^p^k=1
     
    Last edited: Aug 21, 2013
  6. Aug 21, 2013 #5
    Maybe there is other way of proving this statement without using Lagrange's theorem, but, if you want to, check what Axiomer wrote and then the proof is completed using Lagrange's theorem. Anyway, I'll ask my professor to show me an alternative proof. Thanks.
     
  7. Aug 21, 2013 #6
    Yep!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Prime p divides order of group
  1. Groups of order p^2 (Replies: 1)

Loading...