IMO LongList 1985 BRA1-Perimeter and Sum of Diagonal Lengths
Source:
September 10, 2010
geometryperimeterinequalitiestrigonometrytriangle inequalitygeometry unsolved
Problem Statement
A convex quadrilateral is inscribed in a circle of radius . Prove that the difference between its perimeter and the sum of the lengths of its diagonals is greater than zero and less than