Theorem 6.1

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Statement:

Every cyclic group is abelian.

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Proof:

Let $G$ be a cyclic group and let $a$ be a generator of $G$ so that

(1)

\begin{align} G = \langle a \rangle = \{a^{n}\ |\ n \in \mathbb{Z}\}. \end{align}

If $g_{1}$ and $g_{2}$ are any two elements of $G$, there exists integers $r$ and $s$ such that $g_{1} = a^{r}$ and $g_{2} = a^{s}$. Then

(2)

\begin{equation} g_{1}g_{2} = a^{r}a^{s} = a^{r+s} = a^{s+r} = a^{s}a^{r} = g_{2}g_{1}, \end{equation}

so $G$ is abelian.