7

Part of 2005 Sharygin Geometry Olympiad

Problems(1)

concentric circles, A on larger, midpoint of BC on smaller, ABC equilateral

Source: Sharygin 2005 VIII-IX CR 7

Two circles with radii

1

2

have a common center at the point

O

A

of the regular triangle

ABC

lies on the larger circle, and the middpoint of the base

CD

lies on the smaller one. What can the angle

BOC

EquilateralEquilateral Triangleconcentric circlesgeometryangles