(1)OA and OB are the radius of circle.

Given AB = radius of circle

AB = OA = OB

OAB is an equilateral triangle.

AOB = 60˚ [Angle of equilateral triangle = 60˚]

(2)ACB = ½ AOB [The measure of an angle subtended by an arc at a point on the circle is half of the measure of the angle subtended by the arc at the centre.]

ACB = ½ ×60 = 30˚

(3)arc AB = AOB [Measure of a minor arc is equal to the measure of its corresponding central angle.]

arc AB = 60˚

(4)m(arc AB) + m(arc ACB) = 360˚ [Measure of a complete circle is 360°]

60+ m(arc ACB) = 360˚

m(arc ACB) = 360-60 = 300˚

Hence arc(ACB ) = 300˚