I am trying to prove the simplicity of $A\_5$ by showing that every non-trivial normal subgroup $H$ contains a 3-cycle, and therefore is all of $A\_5$ since the 3-cycles all belong to one conjugacy class and all the 3-cycles generate $A\_5$. Now if $H$ contains a 3-cycle already then the proof is done. Otherwise $H$ contains only products of two transpositions or 5-cycles. How can I cook up some general calculation that no matter what I'll always get a 3-cycle from these types of elements?

I've asked a related question [here](https://math.stackexchange.com/q/1757777).