Why unknowns are usually denoted by "X" ? - MathOverflow [closed] most recent 30 from http://mathoverflow.net 2013-06-20T04:54:22Z http://mathoverflow.net/feeds/question/104031 http://www.creativecommons.org/licenses/by-nc/2.5/rdf http://mathoverflow.net/questions/104031/why-unknowns-are-usually-denoted-by-x Why unknowns are usually denoted by "X" ? Alexander Chervov 2012-08-05T16:18:17Z 2012-08-05T22:39:01Z <p>Why unknowns are usually denoted by "X" ? </p> <p>More precisely: is <a href="http://www.ted.com/talks/terry_moore_why_is_x_the_unknown.html" rel="nofollow">this answer</a> really a serious answer or might be a 1 April joke ? Let me sketch it. But please watch it, it is really fun and cool and &lt; 6 min. (Are there any alternative versions?) </p> <p><strong>Answer - because in Spanish there is no sound for "sh" :)</strong></p> <p>Spain was under Arabic influence for a quite a long and played as bridge translating Arabic knowledge to Europe. In Arabic there was some special word for unknowns similar to English "something", but it contained sounds "sh" which was not present in Spanish. It was somehow substituted by "K" and later under further translation to Latin it became "X"...</p> http://mathoverflow.net/questions/104031/why-unknowns-are-usually-denoted-by-x/104046#104046 Answer by Kiran Parkhe for Why unknowns are usually denoted by "X" ? Kiran Parkhe 2012-08-05T20:10:32Z 2012-08-05T20:10:32Z <p>Interesting. Cajori says: "Nor is there historical evidence to support the statement found in Noah Webster's Dictionary, under the letter x, to the effect that 'x was used as an abbreviation of Ar. shei (a thing), something, which, in the Middle Ages, was used to designate the unknown, and was then prevailingly transcribed as xei.'"</p> <p>The Oxford English Dictionary agrees with Cajori.</p> http://mathoverflow.net/questions/104031/why-unknowns-are-usually-denoted-by-x/104058#104058 Answer by Carmen Rovi for Why unknowns are usually denoted by "X" ? Carmen Rovi 2012-08-05T22:39:01Z 2012-08-05T22:39:01Z <p>“Finally, from so little sleeping and so much reading, his brain dried up and he went completely out of his mind.” ― Miguel de Cervantes Saavedra, Don Quijote</p> <p>The name of "Don Quijote" on the original version of Cervantes was spelt "Don Quixote", but the pronunciation was like the Spanish "j". There is no "sh" sound in modern Spanish, and according to some experts, there was none at least to Cervantes times. So the explanation about the "X" sounds plausible. </p>