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  • I have the answer to a question that we've all asked.

  • The question is,

  • Why is it that the letter X

  • represents the unknown?

  • Now I know we learned that in math class,

  • but now it's everywhere in the culture --

  • The X prize, the X-Files,

  • Project X, TEDx.

  • Where'd that come from?

  • About six years ago

  • I decided that I would learn Arabic,

  • which turns out to be a supremely logical language.

  • To write a word or a phrase

  • or a sentence in Arabic

  • is like crafting an equation,

  • because every part is extremely precise

  • and carries a lot of information.

  • That's one of the reasons

  • so much of what we've come to think of

  • as Western science and mathematics and engineering

  • was really worked out in the first few centuries of the Common Era

  • by the Persians and the Arabs and the Turks.

  • This includes the little system in Arabic

  • called al-jebra.

  • And al-jebra roughly translates to

  • "the system for reconciling disparate parts."

  • Al-jebra 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 there are some sounds in Arabic

  • that just don't make it through a European voice box

  • without lots of practice.

  • Trust me on that one.

  • Also, those very sounds

  • tend not to be represented

  • by the characters that are available in European languages.

  • Here's one of the culprits.

  • This is the letter SHeen,

  • and it makes the sound we think of as SH -- "sh."

  • It's also the very first letter

  • of the word shalan,

  • which means "something"

  • just like the the English word "something" --

  • some undefined, unknown thing.

  • Now in Arabic,

  • we can make this definite

  • by adding the definite article "al."

  • So this is al-shalan --

  • the unknown thing.

  • And this is a word that appears throughout early mathematics,

  • such as this 10th century derivation of proofs.

  • The problem for the Medieval Spanish scholars

  • who were tasked with translating this material

  • is 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 a common European language,

  • which is to say Latin,

  • they simply replaced the Greek Kai

  • with the Latin X.

  • And once that happened,

  • once this material was in Latin,

  • it formed the basis for mathematics textbooks

  • for almost 600 years.

  • 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.

  • (Laughter)

  • And I thought that was worth sharing.

  • (Applause)

I have the answer to a question that we've all asked.

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B1 US TED arabic unknown letter spanish european

【TED】Terry Moore: Why is 'x' the unknown? (Why is 'x' the unknown? | Terry Moore)

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    Daniel Chin posted on 2015/05/20
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