Find the radius of the circle.
10 cm
∠BOC=2×30
=60∘ (As angle subtend by an arc at centre is twice the angle subtended by the same arc at the circumference)
Since, OB = OC (radius of the circle)
∠OBC=∠OCB (ΔBOC is an isosceles triangle)
Let, angle ∠OBC=∠OCB=x
So, x+60+x=180∘
2x+60=180
2x=120
x=60∘
So, ΔOBC is an equilateral triangle (all the angles are 60∘)
So, BC = DC = BO = 10 cm
∴ radius of the circle DC = BO = 10 cm