Why “x” is the unknown?

Why “x” is the unknown?

I know we all learn maths in high school, equation like quadratic, cubic function often use x for the variable that we want to solve for. And many of you may have questioned why many text books use “x” to represent the unknown variable?

In mathematics we often use the letter “x” to represent the unknown quantity. But now x is everywhere in our society. People use “x” to represent something that is unexplainable or unknown, such as X-ray, X file and X prize[1]. But why people love to use “x” to represent unknown?


Arabic is a highly logical language, every part of a sentence is precise and carry a lot of information. That is one of the reasons why the basis of mathematics, science and engineering were formed by the Persians and the Arabs and the Turks.

A lot of texts written in Arabic, contained the mathematical ideas finally arrived to Europe around 11th, 12th century. And Europeans were highly interest in translating there text into their language. However there were problems in translating these texts. One problem is that, European cannot pronounce some of the Arabic words without a lot of practises. Also, there are some sounds not really able to represent by the characters in European languages.

One of the examples is that the letter ش which makes the sound “Sheen” and it is the first letter of the word shalan ش ء which means some unknown, undefined thing.  Now we can make it definite by adding the two little l like things at the end اآشء alshalan, the unknown thing. This word appeared in the early mathematical texts and articles, such as the derivation of proofs.

http://www.youtube.com/watch?v=YX_OxBfsvbk @ 2:39

The translator at that time cannot translate this proof in to Spanish because there is no “sh” sound in their language. So they borrowed the “ck” sound from Greek which has letter Kai, and it look really like an X.

Later on, these translated materials translate once again into common European language – Latin. Translator simply replaces the Greek letter Kai (which look like X) with X. And these texts form the basis of mathematics for almost 600 years. And now people get used to using the letter X to represent the unknown.

Information from http://www.ted.com/

[1] X PRIZE Foundation is a nonprofit organization whose mission is to bring about radical breakthroughs for the benefit of humanity, thereby inspiring the formation of new industries and the revitalization of markets that are currently stuck due to existing failures or a commonly held belief that a solution is not possible.

3 Responses to “Why “x” is the unknown?”

  1. frankie says:

    Well there you go. I have a degree in Pure Maths and never knew this…

  2. mzhao says:

    Very interesting!

  3. Talia Hoffman says:

    Etymology is fascinating. It is perplexing that language, the most intimate medium used for thought, isn’t a neutral medium. On the contrary it carries a wealth of history, cultural subjectivity and bias! Useful for taxonomical purposes 😉