condition on $ABC$ for $A'B'C'$ to be equilateral.
Source: 32-th Vietnamese Mathematical Olympiad 1994
February 24, 2007
geometrygeometric transformationreflectiontrigonometrycircumcirclegeometry proposed
Problem Statement
is a triangle. Reflect each vertex in the opposite side to get the triangle . Find a necessary and sufficient condition on for to be equilateral.