In the given figure, O is the center of the circle. If ABOC is a rhombus, find the value of angle BAC.

Soln:
if angle BOC=x then reflex angle BOC=360-x
now angle BAC=(1/2) reflex angle BOC=180-x/2
then
angle BAC=angle BOC
x=180-x/2
x=120
so 
angle BAC=180-120/2=120