2
$\begingroup$

Let $G$ be the orthogonal subgroup $O_2$. Show that the set $\{g \in G : g^2= e\}$ is not a subgroup of $G$

The question before says let $G$ be an abelian group and I can see where I have used that fact. It lets us write $a^2b^2=(ab)^2$ and so $ab \in G$. But I cant find a way to 'get out' of $G$.

  • 2
    HINT: If $g$ and $h$ are elements of the set in question, is it true that the product $gh$ is in there?2012-06-13

2 Answers 2