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Last updated 30/3/2024


How to Sum the Angles of a Triangle
This page attempts to record what is known about the origin and history of the method of summing the angles of a triangle by folding alone. Please contact me if you know any of this information is incorrect or if you have any other information that should be added. Thank you.



As far as I know this simple demonstration by paperfolding that the angles of a triangle sum to 180 degrees was first published in the French magazine L'Illustration 2483 of 27th September 1890 and then included in the second volume of 'La Science Amusante' by Tom Tit (real name Arthur Good), which was published in Paris by Librairie Larousse in 1892.


The demonstration also appears:


In 'Geometrie, Dessin et Travaux Manuels - Cours Moyen', produced under the direction of M E. Cazes, which was published by Librairie Ch. Delagrave in Paris in 1895 under the heading 'La somme des angles d'un triangle vaut deux angles droit' (The sum of the angles of a triangle is equal to two right angles).



Under the heading of 'Angulos del Triangulo' in 'Guia Practica del Trabajo Manual Educativo' by Ezequiel Solana, which was published by Editorial Magisterio Espaņol in Madrid in 1904.



In 'Handicraft in the School', which was issued in four volumes by Gresham Publishing in London in 1910.



In 'Scientific Amusements' (an English translation of some of the material from volumes 2 and 3 of 'La Science Amusante' by Tom Tit) which was published by Thomas Nelson and Sons Ltd in London in 1918.


In 'Ciencia Recreativa' by Jose Estralella, which was published by Gustavo Gili in Barcelona in 1918.



In 'At Home Tonight' by Herbert McKay, which was published by Oxford University Press in London, New York and Toronto in 1940.