Corollary: The supplemental angle of a right angle is another right angle.
(related to Definition: 1.10: Right Angle, Perpendicular Straight Lines)
The supplemental angle of a right angle is another right angle.
Table of Contents
Proofs: 1
Thank you to the contributors under CC BYSA 4.0!
 Github:

 nonGithub:
 @Calahan
 @Casey
References
Adapted from CC BYSA 3.0 Sources:
 Callahan, Daniel: "Euclidâ€™s 'Elements' Redux" 2014
Adapted from (Public Domain)
 Casey, John: "The First Six Books of the Elements of Euclid"