Definition:Proportion/Constant of Proportion

Definition
Let the two real variables $x$ and $y$ be proportional:
 * $\forall x, y \in \R: x \propto y \iff \exists k \in \R, k \ne 0: x = k y$

The constant $k$ is known as the constant of proportion.

Also known as
The constant of proportion is also known nowadays by the less elegant and more cumbersome constant of proportionality.

Some sources use proportionality constant.