Answer:
The length of segment joining the endpoints of the arc is 
Step-by-step explanation:
we know that
In the triangle ABC
see the attached figure to better understand the problem
-----> is the radius of the circle

----> given problem (central angle)
Initially the triangle ABC is an isosceles triangle
Remember that
the sum of the internal angles of triangle must be equal to 
For this particular case, the isosceles triangle ABC becomes an equilateral triangle, as the three angles are equal to 
The equilateral triangle has three equal sides and tree equal angles
so

Hence
The length of segment joining the endpoints of the arc is 