A sector ia a part of a circle. It has two lines and a arc forms the circumference of it. If the angle of the sector is 180 degrees the sector is a semi-circle, the angle of the sector is 360 degrees then the sector is a circle.
perimeter = radius + radius + arc
Radius r = (c^2 / 8h) + (h / 2)
Where C is the chord length, h is the height between the chord and arc.
Area S = arc * radius / 2