# Geometry/Perimeter and Arclength

< Geometry

The circles perimeter can be calculated using the following formula

where the radius of the circle.

The perimeter of a polygon with number of sides abbreviated can be calculated using the following formula

- .

## Arclength of Circles

editThe arclength of a given circle with radius can be calculated using

where is the angle given in radians.

If a curve in has the parametric form for , then the arclength can be calculated using the following fomula

Derivation of formula can be found using differential geometry on infinitely small triangles.