The chord of a circle is equal to its radius. The angle substended by this chord at the minor arc of the circle is
Let AB be the chord of circle equal to radius r
OA = OB = r (Radii)
Therefore,
OA = OB = AB
OBC is equilateral triangle
Each angle = 60°
Hence,
Angle surrounded by AB at minor arc = (Reflex * ∠AOD)
= (360o – 60o)
= 150o