Cyclic Group

Theorem (Cyclic group)

A cyclic group is a group which is equal to one of its cylic subgroups i.e. gG\exists g\in G s.t. G=gG=\langle g\ranglewhere gg is called the generator of GG.

Definition (Cyclic subgroup)

For a group GG, any element gGg\in G one can form a subgroup of all its integer powers g={gk:kZ}\langle g\rangle=\{ g^{k}: k\in\mathbb{Z} \} called the cyclic subgroup generated by g.

Theorem (Finite Subgroups are Cyclic)

Let F\mathbb{F} be any field. Any finite subgroup GG of F\mathbb{F}^{*} is cyclic.

Cor

The only finite subgroups of C\mathbb{C}^{*} are the groups μn\mu_{n} consisting of the nn-th roots of unity with n1n\ge 1.

Cor

If F\mathbb{F} is a finite field, then F\mathbb{F}^{*} is cyclic.

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