# Definition:Proportion/Constant of Proportion

< Definition:Proportion(Redirected from Definition:Constant of Proportion)

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## 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**.

## Sources

- 1966: Isaac Asimov:
*Understanding Physics*... (previous) ... (next): $\text {I}$: Motion, Sound and Heat: Chapter $2$: Falling Bodies: Free Fall