Hyperbolic spiral

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A plane transcendental curve whose equation in polar coordinates is

$$\rho=\frac a\phi.$$

It consists of two branches, which are symmetric with respect to a straight line $d$ (see Fig.). The pole is an asymptotic point. The asymptote is the straight line parallel to the polar axis at a distance $a$ from it. The arc length between two points $M_1(\rho_1,\phi_1)$ and $M_2(\rho_2,\phi_2)$ is


The area of the sector bounded by an arc of the hyperbolic spiral and the two radius vectors $\rho_1$ and $\rho_2$ corresponding to the angles $\phi_1$ and $\phi_2$ is


A hyperbolic spiral and an Archimedean spiral may be obtained from each other by inversion with respect to the pole $O$ of the hyperbolic spiral.

Figure: h048340a

A hyperbolic spiral is a special case of the so-called algebraic spirals.


[1] A.A. Savelov, "Planar curves" , Moscow (1960) (In Russian)
How to Cite This Entry:
Hyperbolic spiral. Encyclopedia of Mathematics. URL:
This article was adapted from an original article by D.D. Sokolov (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article