\begin{definition}[Definition:Geometric Sequence/Common Ratio]
Let $\sequence {x_n}$ be a geometric sequence in $\R$ defined as:
:$x_n = a r^n$ for $n = 0, 1, 2, 3, \ldots$
The parameter:
:$r \in \R: r \ne 0$
is called the '''common ratio''' of $\sequence {x_n}$.
\end{definition}