Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Group theory question

  1. Jan 30, 2008 #1
    1. The problem statement, all variables and given/known data
    true or false:
    If G is a group and g is in G. Then (left) multiplication by g is an isomorphism from G to G


    2. Relevant equations



    3. The attempt at a solution
    I am pretty sure it is true since ax=b always has a solution if a and b are in group. But can someone just confirm this?

    EDIT: sorry, I don't mean isomorphism, I mean bijection
     
    Last edited: Jan 30, 2008
  2. jcsd
  3. Jan 30, 2008 #2

    NateTG

    User Avatar
    Science Advisor
    Homework Helper

    Yes, it's true.
     
  4. Jan 30, 2008 #3
    it's true as nate said, but your reason doesn't tell the whole story(it just gives surjectivity). Try to do it directly, for a fixed g in G, define phi:G->G by phi(x) = gx. Now show it's a bijection.
     
  5. Jan 30, 2008 #4
    gx is in g, and if g1x=g2x then g2inv g1 x = x so g1=g2 so all elements are different, so you can just make couple in your head from every g to every gx.

    I passed group theory this monday =D
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook