N-Dimensional Rays
Definition
Given a nonzero $x \in \R ^n$, the
rays (or
half-lines) through $x$ is
the set
\[
\Set{\lambda x}{\lambda \geq 0}
\]
Examples
There are two rays in $\R $, corresponding to $\Set{x}{x \geq 0}$ and $\Set{x}{x \leq 0}$.