Ok, for this one you only need some very basic knowledge of group theory:

Let be a finitenon-abeliangroup and Let be the number of conjugacy classes of . Prove that with equality if and only if

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- Jan 6th 2009, 11:59 AMNonCommAlgAlgebra, Problems For Fun! (4)
Ok, for this one you only need some very basic knowledge of group theory:

Let be a finite__non-abelian__group and Let be the number of conjugacy classes of . Prove that with equality if and only if - Jan 6th 2009, 02:56 PMchabmgph
- Jan 6th 2009, 03:41 PMNonCommAlg
- Jan 8th 2009, 10:00 PMbulls6x
I will use the fact that the smallest non-abelian group has order 6, which is not hard to show.

Let be the conjugacy classes of . Assume WLOG that the first are non-central.

Suppose Then Thus We will reach a contradiction for each case.

The case is impossible since this would imply were abelian. So assume .

Let with . Let with . Consider

Since and are both noncentral and has order two we know that

Thus

Hence, we have shown that for all But this implies which is a contradiction.

I don't have time to complete the last case. But it is fairly similar. Again use the fact that we know the group structure of and find the similar contradiction. Then use the class equation to get the inequality for . I have not proven the case of equality but I'll leave that for someone else. - Jan 8th 2009, 10:40 PMNonCommAlg
you almost got the idea but you need to put everything together. a quick way to show that is to recall that if G is non-abelian, then is never cyclic. now you need to

combine this result with the class equation to prove the first part. the proof of the second part of the problem comes from the proof of the first part.