Definition:Polar Coordinates/Radial Coordinate
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Let $P$ be a point in a system of polar coordinates where $O$ is the pole.
The length of $OP$ is called the radial coordinate of $P$, and usually labelled $r$.
Also known as
The radial coordinate of $P$ can also be found referred to as the radius of $P$, but this terminology can be ambiguous.
Some sources give this as radius vector.
- 1933: D.M.Y. Sommerville: Analytical Conics (3rd ed.) ... (previous) ... (next): Chapter $\text I$. Coordinates: $2$. Coordinates
- 1968: Murray R. Spiegel: Mathematical Handbook of Formulas and Tables ... (previous) ... (next): $\S 5$: Trigonometric Functions