X is for X

| May 1, 2014

Anyone who has ever taken an algebra lesson is familiar with the request; “Solve for x”. As I was correcting my student’s homework, I started wondering; Why does the letter X represent the unknown?

A brief search directed me towards a talk which has a simple explaination to this question, which comes with a short story;

Algebra is the Arabic term for “system for reconciling disparate parts” and, like much of the western sciences and mathematics, was given birth to during the common era by the Arabs, Turks and Persians. When, in the 11th/12th century, these arabic algebra scripts reached spain, scholars were faced with an arduous challenge; the translation of these texts into European language. At this point, predictable problems arose. Amongst these issues, was the fact that some arabic phonemes simply lack the corresponding letters in spanish. One of such terms which could not be represented by spanish characters was the word ‘ شيء = “thing,” (pronounced “shey”). The spanish language simply doesn’t have a “sh” sound. However, this term appeared frequently in mathematical texts. Therefore, medieval scholars decided to change it to the word “xei”, which could be easily represented and pronounced in European languages, and was soon abbreviated to “x”.

So the reason whythe symbol x commonly denotes an unknown variable is ultimately because: “You can’t say ‘sh’ in spanish!”

Original talk: https://www.ted.com/talks/terry_moore_why_is_x_the_unknown#t-217429