Terry Moore: Why Do We Solve For "X"? Polymath Terry Moore wondered why "X" is the universal unknown in algebra. He dove into the history of numbers to come up with an unexpected answer.
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Why Do We Solve For 'X'?

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Why Do We Solve For 'X'?

Why Do We Solve For 'X'?

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But before we go any further trying to solve for X, a more basic question - what is X?

TERRY MOORE: X is the unknown.

RAZ: But why X? Why not another letter? Terry Moore wanted to find out.

MOORE: Yes, exactly.

RAZ: Terry directs an organization that promotes mathematics. And he told the story of why X is X on the TED stage.


MOORE: 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-jabra. Al-jabra roughly translates to the system for reconciling disparate parts. Al-jabra finally came into English as algebra. The Arabic texts containing this mathematical wisdom finally made their way to Europe - which is to say Spain - in the 11th and 12th century. And when they arrived, there was tremendous interest in translating this wisdom into a European language.

RAZ: Ok, so they start translating algebra from Arabic into Spanish. So what's the unknown in Arabic? What's the X?

MOORE: It was originally the word sheiun (ph), which means something.

RAZ: Something.

MOORE: Something - some undefined thing.


MOORE: The problem for the medieval Spanish scholars who were tasked with translating this material is that the word sheiun can't be rendered into Spanish because Spanish doesn't of that S-H - that sh sound. So by convention, they created a rule in which they borrowed the C-K sound - the cuh sound - from the classical Greek in the form of the letter Chi. Later, when this material was translated into a common European language - which is to say Latin - they simply replaced the Greek Chi 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 shh in Spanish.


MOORE: And I thought that was worth sharing.


RAZ: So this was kind of like a big misunderstanding, really. Like, it could've been Y. Or it could've been Q or B.

MOORE: It's certainly possible. And to some degree, it was arbitrary. But the origin is that Arabic sheiun, which means something. Had they chosen a different word, we probably would be referring to the unknown quantity by some other letter.

RAZ: Yeah. What if X was B? Then everything would be B. We'd have like, the B-Men and Malcolm B and B-marks-the-spot and the B-Files.

MOORE: That's right. And Project B.

RAZ: That would ruin everything. Thank the gods it was the X.

MOORE: Well, we're used to that now.

RAZ: Do you like algebra?

MOORE: Yes, I love algebra.

RAZ: Why?

MOORE: Because it's beautiful.

RAZ: How, how? I keep hearing that. I hear mathematicians say it's beautiful. And then, you, like, see these movies about these crazy geniuses and they're scrawling on the chalkboards. It is kind of nice, actually. But I still don't get it.

MOORE: I think that's a matter of temperament. There're some people to whom a mathematical proof appears as a thing of beauty. It speaks of a higher truth. It speaks of a harmony to knowledge. The fact that it works at all - let alone that we can understand it - speaks to a larger category of existence and knowledge.

RAZ: Terry Moore - you can see his full talk - Why Is X The Unknown? - at ted.npr.org.

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