G1

Part of 2015 Costa Rica - Final Round

Problems(1)

MMO 063 Moscow MO 1940 AD + BD = DC in an inscribed equilateral

Source:

A, B, C

are vertices of an equilateral triangle inscribed in a circle. Point

D

lies on the shorter arc \overarc {AB} . Prove that

AD + BD = DC

Equilateralarcgeometry