Condition for Linear Operation on Complex Numbers to be of Finite Order

Theorem

Let $A$ be the operation on the complex numbers $\C$ defined as:

$\map A x = \alpha x + \beta$

Then $A$ is of finite order greater than $1$ if and only if $\alpha$ is a root of unity other than $1$.

Sources

• 1964: Walter Ledermann: Introduction to the Theory of Finite Groups (5th ed.) ... (previous) ... (next): Chapter $\text {I}$: The Group Concept: Examples: $(3)$