{{Information |description ={{en|1=Visual proof of Viviani's theorem drawn by CMG Lee. 1. Nearest distances from point P to sides of equilateral triangle ABC are shown. 2. Lines DE, FG, and HI parallel to AB, BC and CA, respectively, define smaller triangles PHE, PFI and PDG. 3. As these triangles are equilateral, their altitudes can be rotated to be vertical. 4. As PGCH is a parallelogram, triangle PHE can be slid up to show that the altitudes sum to that of triangle ABC.}} |date...
Visual proof of Viviani's theorem drawn by CMG Lee. 1. Nearest distances from point P to sides of equilateral triangle ABC are shown. 2. Lines DE, FG, and HI parallel to AB, BC and CA, respectively, define smaller triangles PHE, PFI and PDG. 3. As these triangles are equilateral, their altitudes can be rotated to be vertical. 4. As PGCH is a parallelogram, triangle PHE can be slid up to show that the altitudes sum to that of triangle ABC.