When a circle's diameter is 1 unit, its circumference is pi (∏) units.

Circumference = ∏ * diameter
Circumference = 2∏ * radius

∏ = 3.14159



sin(angle)=O/H
cos(angle)=A/H
tan(angle)=O/A

degrees=radians*(180/∏)
radian=degrees*(∏/180)