Definition:Geometric Sequence/Common Ratio

Definition
Let $\left \langle{x_n}\right \rangle$ be a geometric progression in $\R$ defined as:
 * $x_n = a r^{n-1}$ for $n = 1, 2, 3, \ldots$

The parameter:
 * $r \in \R: r \ne 0$

is called the common ratio of $\left \langle{x_n}\right \rangle$.