Arc Length, Sector and Segment Area
Reminder from Year 9/10
Area of circle = pr2
Circumference = πd or 2πr
A sector is part of the circle area.
Radians = α(degrees) × π / 180º
Please note that our formulae in the green box all use radians.
Notes: Click this link for a tutorial on the different aspects of circle trig.
Khan Institute explanation of radians.