Geometry/Perimeter and Arclength
The circles perimeter can be calculated using the following formula
where and the radius of the circle.
The perimeter of a polygon with number of sides abbreviated can be caculated using the following formula
Arclength of Circles 
The arclength of a given circle with radius can be calculated using
where is the angle given in radians.
If a curve in have a parameter 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.