# Astroid (Perimeter)

## Description

An astroid is a particular mathematical curve: a hypocycloid with four cusps. The astroid is a real locus of a plane algebraic curve of genus zero. The curve has a variety of names, including tetracuspid, cubocycloid, and paracycle. It is nearly identical in form to the evolute of an ellipse. An astroid created by a circle rolling inside a circle of radius “a” will have a perimeter depended on radius “a”.

Related formulas## Variables

P | Perimeter of the astroid (m) |

a | The radius of the rolling circle (m) |