- Draw a line from B to O (circle centre)
- BO = OD (both radii) and now ODB is iscoceles triangle
- EAD = ADB = DBO = 30 degrees
- angle of arc at centre = 120 degrees (180-30-30)
So 120/360 (2* Pi * r) = 4 * Pi
solving you get r = 6
Area = 36 Pi
thats one way of solving it ....u can also solve this by using the "angle at center theorm".....ie
the angle subtended by the arc at the center is twice the angle subtended by it at any other point on the circle.
arc BCD makes angle 60 deg at a : angle BAD = 60. therefore the angle made by the same arc at center :ang BOD = 120 deg.
so using ur formula....4 pi = 2pi *r* *[120/306]
r = 6
area = pi*r*r
Second cut is the deepest cut!!!:P