Arc AB is of the circumference of a circle. What is the radian measure of the central angle?

The arc AB is 1/6 of the circumference of a circle and we have the equation.

∅=s/r

where ∅ is the central angle in radian, from the given we know that s/r is equal to 1/6

Therefore, ∅=1/6 which the central angle of the circle.