Heiberg 1908, стр. 177–178 Heiberg, Johan Ludvig (1908), Heath, T. L., ур., Euclid, The Thirteen Books of Euclid's Elements, 1, Cambridge: Cambridge University Press.
D. Zwillinger, ур. (1995), CRC Standard Mathematical Tables and Formulae, Boca Raton, FL: CRC Press, стр. 270 as cited in Weisstein, Eric W. „Exterior Angle”. MathWorld.
worldcat.org
Altshiller-Court, Nathan (2007) [1952], College Geometry: An Introduction to the Modern Geometry of the Triangle and the Circle (2nd изд.), Courier Dover, ISBN978-0-486-45805-2, OCLC78063045