# 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.