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Proving group commutativity

  1. Jan 28, 2010 #1
    I have a homework problem that states: Let G be a group with the following property: Whenever a,b and c belong to G and ab = ca, then b=c. Prove that G is abelian.

    I started with the hypothesis ab=ca and solved for b and c using inverses. I found b=(a-1)ca and c=ab(a-1). Because the hypothesis says b=c I set them equal. (a-1)ca=ab(a-1). But I'm having trouble getting anywhere useful after that. Hints or suggestions if I'm on the right track???
     
  2. jcsd
  3. Jan 28, 2010 #2
    Suppose G is Abelian and it doesn't have that property. Show a contradiction that G must not be Abelian.

    Can you show a contradiction?
     
  4. Jan 28, 2010 #3
    So I should try assuming its not abelian and try proving that if ab=ca, then b equals c??
     
  5. Jan 28, 2010 #4
    Suppose G is Abelian and it doesn't have that property.

    I already wrote the first line for you.
     
  6. Jan 28, 2010 #5
    Start with [tex]aba^{-1}=c[/tex] (c is just some element of the group). Now, if you right-multiply by a, and apply the hypothesis, what do you conclude?
     
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