# What is this math symbol called? [closed]

My professors use a symbol $$x_0$$ and they pronounce it as x not or x nod, I am not sure what the exact name is because they have thick accents. I have tried looking this up on the Internet but I could not find an answer. Does anyone know what this is called?

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## closed as off-topic by Grigory M, user1096156, Swapnil Tripathi, user21820, WLOGJan 5 '15 at 13:42

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "This question is not about mathematics, within the scope defined in the help center." – Grigory M, user1096156, Swapnil Tripathi, user21820
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They will likely be saying "x naught", naught being a synonym for zero. – Matthew Pressland Feb 7 '13 at 17:43
'x naught'? as in 'x zero' ? – Dan Rust Feb 7 '13 at 17:43
Please oh please, if your professor says something and you cannot even make out what he is saying, let alone what it means, please oh please ask him! There are very few more intensive wastes of time than you sitting in a class and his giving the class without even this minuscule piece of communication being successful! – Mariano Suárez-Alvarez Feb 7 '13 at 19:18

It's probably x-naught, synonym for "x sub zero", it's used when you refer to an starting point for variable $x$, for example in physics, if you have a particle moving on the $x$ axis, you will always find $x_0$ for the initial position.

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I call it as you said, x sub zero. – Babak S. Feb 7 '13 at 17:52

They actually call it x-naught. I believe it comes from British English. Kind of like how the Canadians call the letter z "zed". All it means is "x sub zero", just another way of saying the same thing. It does flow better though, I think. "sub zero" just takes so much more work to say. I do think "naught" and "not" have similar meaning though - the absence of something, some value or quality. Im sure there is a linguistic connection.

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I imagine it is British English, although it's less common now I think to say "naught" for 0. We do still also call z "zed" though! – Matthew Pressland Feb 7 '13 at 17:52
"Zed" is etymologically more reasonable; it is an alteration of Greek "zeta". Nobody knows exactly when or why Americans started calling it "zee". – MJD Feb 7 '13 at 18:19
You two do realize that this post had nothing to do with zed, right? I dont know why youre going on about it. I only used it as an example of how different dialects have adopted different terms and pronunciations for the same things. If you want to be relevant, explain the root etymological source of "naught". – CogitoErgoCogitoSum Feb 10 '13 at 20:31