Question
Let $G$ be an abelian group.Let $H=\left\{x \in G: x=y^{2}\right.$ for some $\left.y \in G\right\}$, that is, let $H$ be the set of all the elements of $G$ which have a square root. Prove that $H$ is a subgroup of $G$.
Step 1
If $x_1, x_2 \in H$, then there exist $y_1, y_2 \in G$ such that $x_1 = y_1^2$ and $x_2 = y_2^2$. Therefore, $x_1x_2 = y_1^2y_2^2 = (y_1y_2)^2$. Since $y_1y_2 \in G$, we have $x_1x_2 \in H$. Show more…
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