**Tags: Euclid, Elements, Geometry, Proposition, Proof**

Tags: Euclid, Elements, Geometry, Equilateral, Triangle

Tags: Euclid, Elements, Geometry, Parallelogram, Triangle

Tags: Euclid, Elements, Geometry, Parallelogram, Triangle, Angle

Tags: Euclid, Elements, Geometry, Pythagorean, Theorem

Tags: Euclid, Elements, Geometry, Square, Quadrilateral