The segment joining either pair of opposite angles of a square, rectangle, rhombus, rhomboid , or trapezium is called a diagonal.
Propositions: 1 2
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"