# Abstract Algebra

1. Sep 17, 2008

### Thorn

If G is an abelian group of order (p^t)m, and (p,m)=1, show that G(p) has order p^t

and G(p) = {a e G| |a|=p^m where m is a natural number}

any suggestions?

2. Sep 18, 2008

### morphism

What do you have to work with? This problem is trivial if you've developed enough tools.

You can also do this with your "bare hands" if you want to. What have you tried so far?

Last edited: Sep 18, 2008
3. Sep 18, 2008

### Thorn

Geez...I have no idea where to start...

Ok, I was looking at a lemma...

"Let G be an abelian group and a $$\in$$ G and is an element of finite order. Then a = a1+a2+...+ak, with ai an element of G(pi), where p1,....,pk are the distinct positive primes that divide the order of a"

.... now G(p) is only the set of all elements whose order is some power of p... I was thinking you could use that lemma to show that G(p) has power pt ...seems like that could help somehow.. but it seems I need to use the fact that (p,m)=1 ...this surely means that (pt,m)=1 which means you can write 1=pt*u + m*v...for some numbers u,v... and I have no idea where to go...

4. Sep 18, 2008

### Thorn

Well...Actually, I could use Cauchy's theorem for Abelian Groups...

"If G is a finite abelian group and p is a prime that divides |G|, prove that G contains an element of order p....

we know that p divides |G|...and p2 divides the order of G...and so on and so on until we have pt divides the order of G...so all these elements exist in G(p)..then use the (p,m)=1 to show that each one of these elements is uniquely the product of m with some interger...I think that is it...

5. Sep 19, 2008

### morphism

Does Cauchy's theorem imply that if p^m divides |G|, then G contains an element of order p^m?

The fact that G is abelian is vital here. First note that G(p) is a subgroup of G. Next note that G(p) has order a power of p, by Cauchy. If |G(p)| isn't p^t, then we can consider the group G/G(p). G/G(p) is still abelian, and p divides |G/G(p)|. Apply Cauchy's theorem again to get an element g+G(p) of order p. Now what?

6. Sep 20, 2008

### mathwonk

you might start by trying to prove there is an element of order p, if t>0.