Proving Cauchy's Theorem with induction

In summary, to prove that if a prime number divides the order of a finite abelian group G, then G has an element of order p, we use induction on the order of G and the fact that G/H has a smaller order than G if H is non-trivial.
  • #1
beachbum300
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Homework Statement



If p is a prime and p divides the order of G where G is a finite abelian group, then G has an element of order p. Prove without using the Fundamenthal Theorem for Finitely Generated Abelian Groups.
Hint 1: Induct on the order of G
Hint 2: Note that G/H has a smaller order than G if H is non-trivial

Homework Equations





The Attempt at a Solution


P(n): If the order of G=n and p divides the order of G, then G has an element of order p.
Base Case:
Consider n=1. Vacuously true.
Consider n=2. Since 2 is prime and 2 divides 2, then G has an element of order 2
Consider n=3. Since 3 is prime and 3 divides 3, then G has an element of order 3.
Inductive Step:
Assume P(k) is true for 0<k<n where n>3.
This is where I'm not sure of what to do next. Any suggestions?
 
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  • #2
Take any non-identity element of G, say a, and use [itex]n=[G:<a>]|<a>|[/itex].
 

1. How is Cauchy's theorem proved using induction?

Cauchy's theorem is proved using mathematical induction, which is a technique for proving that a statement holds for all natural numbers. In this case, we use induction to show that the statement holds for all n, where n is a positive integer.

2. What is the statement of Cauchy's theorem?

The statement of Cauchy's theorem is that for any finite group G, the number of elements in G that satisfy a given polynomial equation is a multiple of the group's order.

3. What is the role of the base case in proving Cauchy's theorem with induction?

The base case is the first step in the induction process, where we show that the statement holds for the smallest possible value of n. In this case, the base case is when n=1, which is the smallest possible order of a group. By showing that the statement holds for n=1, we establish a foundation for our induction proof.

4. How does the inductive step work in proving Cauchy's theorem?

The inductive step is where we assume that the statement holds for some value of n, and then use this assumption to show that it also holds for n+1. In the proof of Cauchy's theorem, we use the fact that the statement holds for n to show that it also holds for a larger group with order n+1. This completes the inductive step and allows us to extend the proof to all natural numbers.

5. What are the key ideas in the proof of Cauchy's theorem with induction?

The key ideas in the proof of Cauchy's theorem with induction are using the divisibility of group orders, the fact that elements of a group can be written as a product of cyclic subgroups, and the use of the pigeonhole principle. These ideas, combined with the base case and inductive step, allow us to prove Cauchy's theorem for all finite groups.

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