Suppose G is a group and $\displaystyle Z(G)=\{a\in G | ax=xa, \forall x\in G \}$. Show that $\displaystyle G/Z(G)$ is cyclic, then G is abelian
$\displaystyle G\slash Z(G)\,\, cyclic\, \Longrightarrow G\slash Z(G)=\left<xZ(G)\right>\,\,\,\mbox{for some}\,\,x\in G\,\Longrightarrow$
$\displaystyle \forall g\in G\,\,\exists\, n_g \in\mathbb{Z}\,\,s.t.\,\,gZ(G)=x^{n_g}Z(G)\Longrig htarrow\,\exists z_g\in Z(G)\,\,s.t.\,\,g=x^{n_g}z_g$
Well,now take two elements in G, express them as described above and prove they commute.
Tonio