I’m sure every college student has heard of this little mathematics thing called “algebra”. But did you know it comes from a little system in Arabic called ‘al-jebr’?
Al-jebr roughly translates to “the system for reconciling disparate parts.”
Arabic texts containing this mathematical wisdom made their way to Spain in the 11th and 12th centuries. When they arrived there was a lot of interest in translating them into a European language. One of the biggest problems in doing this is that some sounds in Arabic tend not to be represented by characters available in European languages.
SHeen for exmaple, makes the sound we think of as SH — “sh.” It’s also the very first letter of the word “shalan”, which means “something”– some undefined, unknown thing.
You can make this definite in Arabic by adding the article “al.” So this is “al-shalan” literally means “the unknown thing”. Al-shalan appears throughout early mathematics, and the problem for the Medieval Spanish scholars that were translating the works was that the letter SHeen and the word SHalan can’t be rendered into Spanish because Spanish doesn’t have that SH, that “sh” sound. So by convention, they created a rule in which they borrowed the CK sound, “ck” sound, from the classical Greek in the form of the letter Kai.
Later when this material was translated into Latin, they replaced the Greek Kai with the Latin X.
And once the material was in Latin, it formed the basis for mathematics textbooks for almost 600 years.
So why is it that X is the unknown?
Because you can’t say “sh” in Spanish.