The Parallelogram Law Proven Simply at Dreamshire blog The Parallelogram Law: A Proof Without Words at cut-the-knot A generalization of the "Parallelogram Law/Identity" to a Parallelo-hexagon and to 2n-gons in General - Relations between the sides and diagonals of 2n-gons (Douglas' Theorem) at Dynamic Geometry Sketches, an interactive dynamic geometry sketch.
Комутативност Простор на внатрешен производ Нормиран векторски простор Поларизационен идентитет „Parallelogram Law“ од Ерик В. Вајсштајн - MathWorld (англиски) The Parallelogram Law Proven Simply at Dreamshire blog The Parallelogram Law: A Proof Without Words at cut-the-knot A generalization of the "Parallelogram Law/Identity" to a Parallelo-hexagon and to 2n-gons in General - Relations between the sides and diagonals of 2n-gons (Douglas' Theorem) at Dynamic Geometry Sketches, an interactive dynamic geometry sketch.