Third Millennium International Mathematical Olympiad 2009
Grade 10-12
Problem 4
By definition, the shortest pass between two points on the surface of a cube is the shortest broken line on the surface of the cube joining the two points. (Which is a straight line segment whenever the given points lie on the same face.) Three shortest passes joining three points split the surface of a cube into two regions. The region with the smallest area is called a triangle. Find the largest area of a triangle on the surface of a unit cube.