On proofs of the lrrationality of the square root of 2

Document Type : Research Paper

Authors

1 Department of Computer Science, Birjand University of Technology, Birjand, Iran

2 Department of Basic Sciences, Birjand Girls' Technical and Vocational School, Technical and Vocational University, Birjand, Iran

Abstract

This article reviews some of the most famous proofs of the irrationality of the square root of 2. Given the nature of defining irrational numbers, we will see that most proofs (except Proof No. 23) have been done either directly or indirectly using proof by contradiction. We have tried to mention cases that have the potential to be generalized to a proof for the irrationality of the square root of other numbers as well. Some proofs have been slightly modified to ensure clarity of the resulting text. Additionally, some new results have been obtained in certain cases.

Keywords


[1] S. Shahshahani, Differential and Integral Calculus 1, second edition, Fatemi Publications, (2008)
[2] K. V. Fritz, The discovery of incommensurability by Hippasus of Metapontum, Ann. of Math., Second Series, 46 (1945) 242–264.
[3] Aristotle (Translator : R. Smith), Prior Analytics, Hackett Publishing Company, (1989).
[4] B. L. Van Der Waerden, Science Awakening I, Springer Netherlands, (1975).
[5] T. M. Apostol, Irrationality of the square root of two - a geometric proof, Amer. Math. Monthly, 107 (2000) 841–842.
[6] O. Neugebauer, The Exact Sciences in Antiquity, 2nd. edition, Brown University Press, Providence, R. I., (1957).
[7] O. Neugebauer, Mathematische Keilschrift-Texte/Mathematical Cuneiform Texts, Springer-Verlag Berlin Heidel-berg, (1935).
[8] V. C. Harris, Terminal digit proof that √ 2 is irrational, The Mathematical Gazette, 53 (1969) 65.
[9] V. C. Harris, On proofs of the irrationality of √ 2 , The Mathematics Teacher, 64 (1971) 19–21.
[10] H. Eves, The irrationality of √ 2 , The Mathematics Teacher, 38 (1945) 317–318.
[11] E. T. Whittaker and G. N. Watson, A Course of Modern Analysis, 4nd edition, Cambridge University Press, (1927).
[12] M. V. Subbarao, A simple irrationality proof for quadratic surds, Amer. Math. Monthly, 75 (1968) 772–773.
[13] E. Halfar, The irrationality of √ 2 , The American Mathematical Monthly, 62 (1955) 437.
[14] R. Dedekind (Translator: W. W. Beman), Essays on the Theory of Numbers, Dover Publications, (1963).
[15] J. Conway and V. Neumann, The power of mathematics, in Power (Darwin College Lectures), editors: A. Black-well, D. MacKay, Cambridge University Press, (2005).
[16] S. J. Miller and D. Montague, Picturing Irrationality, Math. Mag., 85 (2012) 110–114.
[17] G. Cairns, Proof without words: √ 2 is irrational, Math. Mag., 85 (2012) 123.
[18] J. Stillwell, Mathematics and Its History, 3nd edition, Springer-Verlag New York, (2010).
[19] D. Kalman, R. Mena, S. Shahriari, S. J. Miller and D. Montague, Variations on an irrational theme-geometry, dynamics, algebra, Math. Mag., 70 (1997) 93–104.
[20] M. Laczkovich, Conjecture and Proof, Mathematical Association of America, (2001).
[21] V. H. Moll, Numbers and Functions: From a classical-experimental mathematician’s point of view, Mathematica Association of America, (2012).
[22] F. V. Waugh and M. W. Maxfield, Side and diagonal numbers, Math. Mag., 40 (1967) 74–83.
[23] T. M. Liggett and P. Petersen, The law of large numbers and √ 2 , Amer. Math. Monthly, 102 (1995) 31–35.
[24] J. Conway and R. Guy, The Book of Numbers, Springer-Verlag New York, (1996).
[25] G. C. Berresford, A simpler proof of a well-known fact, Amer. Math. Monthly, 115 (2008) 524.
[26] N. C. Ferreno, Yet another proof of the irrationality of √ 2 , Amer. Math. Monthly, 116 (2009) 68–69.
[27] R. W. Floyd, What else Pythagoras could have done, Amer. Math. Monthly, 96 (1989) 67.
[28] D. Hensley, Continued Fractions, World Scientific Publishing, (2006).
[29] J. A. C. Araujo, A difference equation leading to the irrationality of √ 2 , Amer. Math. Monthly, 121 (2014) 443.
[30] K. K. Usadi and K. Mikhail, Meaning in classical mathematics: is it at odds with intuitionism?, Intellectica, 56
(2011) 223–302.
[31] S. M. A. Khatami, A model theoretic proof of the irrationality of √ 2 , Amer. Math. Monthly, (submitted).
[32] A. Bogomolny, Square root of 2 is irrational, Cut the Knot, (1996–2018).