Plane curves which usually go around one point (or around several points), moving either towards or away from it (them). One distinguishes two types: algebraic spirals and pseudo-spirals.
Algebraic spirals are spirals whose equations in polar coordinates are algebraic with respect to the variables and . These include the hyperbolic spiral, the Archimedean spiral, the Galilean spiral, the Fermat spiral, the parabolic spiral, and the lituus.
Pseudo-spirals are spirals whose natural equations can be written in the form
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Spirals. Encyclopedia of Mathematics. URL: http://www.encyclopediaofmath.org/index.php?title=Spirals&oldid=18060