I'm just starting a course on group theory and the question in struggling with is as follows:

Let $G$ be a finite Abelian group and let $x\in G$. Proof: $\prod_{g\in G}xg=\prod_{g\in G}g$

I've tried a couple things, since the group is Abelian we have: $\prod_{g\in G}xg=x^{\left|G\right|}\prod_{g\in G}g$. I know for a fact that $x^{\left|G\right|}=e$ however this is only proved using Lagrange's Theorem which is still about 5 weeks away and I can't use right now. So my question is either:

  1. Is there another way, that is without Lagrange's Theorem, to prove that $x^{\left|G\right|}=e$?
  2. Do you have any tips for solving this question?

Thanks is advance!


If the elementns of $G$ are $g_1,g_2,g_3,\ldots, g_n$, then $xg_1, xg_2, \ldots, xg_n$ are the same elements, just possibly in a permuted order.

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  • $\begingroup$ I am sorry but you should justify your answer by the fact that $g \to xg$ is bijective because it possesses an inverse which is $g \to x^{-1}g$. $\endgroup$ – Jean Marie Feb 21 '19 at 8:20

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