USAMO 2003 Problem 2
Source:
September 27, 2005
USAMOtrig identitiesLaw of Cosines
Problem Statement
A convex polygon in the plane is dissected into smaller convex polygons by drawing all of its diagonals. The lengths of all sides and all diagonals of the polygon are rational numbers. Prove that the lengths of all sides of all polygons in the dissection are also rational numbers.