Proof: By Euclid
(related to Corollary: Rectangle as a Special Case of a Parallelogram)
This follows immediately from Prop 1.34 and the definition of a rectangle.
Adapted from CC BY-SA 3.0 Sources:
- Callahan, Daniel: "Euclid’s 'Elements' Redux" 2014
Adapted from (Public Domain)
- Casey, John: "The First Six Books of the Elements of Euclid"