Answer: so, if l is the length of the arc, r is the radius of the circle and θ is the angle subtended at the centre, then; θ = l/r, where θ is in radians
Central angle, θ = (Arc length × 360º)/(2πr) degrees or Central angle, θ = Arc length/r radians, where r is the radius of the circle. The formula is Degrees = Radians × 180 / π and it can be used for both positive and negative values. The sector of a circle is a slice of a circle, bound by two radiuses and an arc of the circumference. We identify sectors of a circle using their central angle. The central angle is the angle between the two radiuses. Sectors with a central angle equal to 90° are called quadrants.