Each of the base angles of a isosceles triangle is 58° and the verticles of the triangle lie on a circle. Determine the angle which the base of the triangle subtends at the centre of the circle.

A.
128^{o} 
B.
16^{o} 
C.
64^{o} 
D.
58^{o}
Correct Answer: Option A
Explanation
Base angle of the triangle = 58°.
The third angle = 180° – (58° + 58°)
= 64°
Angle subtended at the centre = (2 times 64° = 128°) (angle at the centre is twice the angle at the circumference).