- Daniel Ethier
This is a demonstration of a simple proof without words of Fagnano's Problem. The proof uses reflection to show that the minimal perimeter triangle that can be inscribed in an acute triangle is the one with its vertices at the feet of the altitudes of the acute triangle. You can drag points A, B, and C to modify the original triangle (in the middle). The red line will remain straight, and so the shortest path. The red line is the inscribed triangle, unwrapped by the reflections.