Find the length of the arc of a circle of diameter 42 cm which subtends an angle of 60° at the centre.
Diameter of circle = 42 cm
⇒ Radius of circle = cm = 21 cm
Angle subtended at the centre = 60°
∵ Length of arc = × 2πr
= 22 cm
Hence, the length of the arc is 22 cm.