Show that all simple groups of order 60 are isomorphic to A5.

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In summary, if G is a simple group of order 60, then there exists a homomorphism from G to S5 with kernel A5, making G isomorphic to A5. This is proven by showing that A5 is the only subgroup of order 60 in S5, and since G is simple, it must be isomorphic to A5.
  • #1
glacier302
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Prove that if G is a simple group of order 60, then G is isomorphic to A5.

So far, I have shown that there is a subgroup of G with index 5. I know that with this information I should be able to show that G is isomorphic to A5, but I'm not sure how...
 
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  • #2
Prove that if G is a simple group of order 60, then G is isomorphic to A5.

So far, I have shown that G has a subgroup of index 5. If I call these 5 cosets K1, K2, K3, K4, and K5, then G acts by conjugation on these cosets, and there is a homomorphism from G to S5. I'm not sure how to proceed from there...
 
  • #3
I think this is right.
As you said, there's a homomorphism from G to S5. The image of the G is a subgroup of S5, call it H. This subgroup can't be S5 itself, since S5 has 120 elements, and A5 has only 60. If |H| < 60 then the kernel of the homomorphism is more than just the identity, and is normal in G. But G is simple, so |H|=60, i.e. H=A5, so then G=A5.
 
  • #4
i guess you should check that A5 is the only subgroup of order 60 in S5.
 
  • #5
Thank you, I think I figured it out : )
 

1. What is the significance of simple groups of order 60?

Simple groups of order 60 are important in group theory because they are the smallest non-abelian simple groups. They also have interesting properties and connections to other mathematical concepts.

2. How do you prove that all simple groups of order 60 are isomorphic to A5?

To prove this statement, we first need to show that any simple group of order 60 must have a normal subgroup of order 12. This can be done using the Sylow theorems. Then, we show that this normal subgroup is isomorphic to A5 by constructing a specific isomorphism between the two groups.

3. Why is A5 the only simple group of order 60?

This is because A5 is the only group of order 60 that has a normal subgroup of order 12. Any other group of order 60 would have a different normal subgroup, and therefore would not be isomorphic to A5.

4. Can you give an example of a simple group of order 60?

One example of a simple group of order 60 is the alternating group A5, which consists of all even permutations on 5 elements. This group has order 60 and is isomorphic to A5.

5. Are there any other ways to prove that all simple groups of order 60 are isomorphic to A5?

Yes, there are other ways to prove this statement. One approach is to use the classification of finite simple groups, which states that any simple group of order less than 60 must be cyclic or alternating. Another approach is to use representation theory and show that any simple group of order 60 must have a faithful irreducible 5-dimensional representation, which is unique up to isomorphism and is equivalent to A5.

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