Letter X in Mathematics

We all have a question to be answered in mathematics. The question is, where does this (X) come from? Why is the letter X used to express the unknown in mathematics?

We saw this letter X in math lessons, but now it's almost everywhere in the world -- The X-Files, Project X, TEDx. Where'd that come from?

Arabic is a supremely logical language. Writing a word, phrase, or sentence is like crafting an equation because every part is exact and carries much information. That's one of the reasons we've come to think of Western science, mathematics, and engineering was really worked out by the Persians, the Arabs, and the Turks in the first centuries of the Common Era.

This includes the little system in Arabic called al-jebra (الجبر). And al-jebr roughly translates to "the system for reconciling disparate parts." Al-jebr finally came into English as algebra. One example among many.

The Arabic texts containing this mathematical wisdom finally made their way to Europe -- which is to say Spain -- in the 11th and 12th centuries. And when they arrived, there was tremendous interest in translating this wisdom into a European language.

But there were problems. One problem is that some sounds in Arabic don't make it through a European voice without much training and practice.

For example, this is the letter sheen (ش), which makes the sound SH -- "sh". It's also the first letter of the word (شیء) shayun, which means "something", just like the word "something" in English -- some unknown, undefined thing.

Now in Arabic, we can make this definite by adding the definite article "al". So this is al-shayun (الشیء) - the unknown thing-. And this is a word that appears during early mathematics.

Medieval Spanish scholars who were tasked faced problems with translating this material. The problem is that the letter sheen and the word shayun can't be rendered in 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 classical Greek in the form of the letter Kai.

Later, when this material was translated into a common European language, which is to say Latin, they simply replaced the Greek Kai with the Latin X. Once that happened, once this material was in Latin, it formed the basis for mathematics textbooks for almost 600 years.

For the first time, René Descartes used the letter x in the book La Géométrie (1637). And in the tradition of using x, y and z to express an unknown.

But now we have the answer to our question. Why is it that X is the unknown? X is the unknown because you can't say "sh" in Spanish.