Viviani's theorem.
Viviani's theorem again with the rotation method
This theorem, attributed to Vincenzo Viviani (1622-1703), gives a remarkable property of equilateral triangles. Theorem. The perpendiculars to the sides from a point on the boundary or within an equilateral triangle add up to the height of the triangle.
This proof [Kawasaki, 2005] uses only rotation to establish the theorem. |