How Did X Become the Unknown (and so much else)? 

So now you know how X took over math, but let's give it some love in regular language: Post your favorite word containing X below! Mine is *equinox*

X also implies precision. In carpentry and on maps, it allows one to define an exact point with two crossing lines.

Elon Musk has a weird obsession with X

8:10 X is important in printing because it reaches all 4 corners equally. It is the standard by which all letters are measured in setting a typeface. From it you can calculate descenders (e.g. length of the tail on letter 'g'), ascenders (e.g. height of a letter 'h') and differing widths of letters (e.g. 'i' is thinner than 'd'), to set the spacing of words and lines when letters were physical blocks plated with ink. The principles still apply in the digital equivalent. Different typefaces take up different amounts of space on a printed page (or screen) depending on their dimensions relative to the standard 'X'.

Saying X three times, reveals the mystery of creation of life too. Very mysterious.

I always thought we used x because it's rare in natural language use so that you can easily distinguish math from any letters used for the description.

6:30 Actually, in older Spanish (as in Modern Portuguese), a Sh sound did exist, which was spelt with an X. It fused with Spanish J in sound, and was thus replaced with J (except in some words). This is why in many indigenous languages of Latin America, the Sh sound is spelled with X, and why the name "Mexico", which comes from Nahuatl, is pronounced in Spanish as if it is Mejico.

Given Descartes's decision to use letter at the beginning of the alphabet for known constants and end of the alphabet for variables, it makes sense to me that x is used more than z. I bet "a" shows up more than "c" too.

At 2:35 The first '=' at the bottom should instead be '+' and at 5:12 it should be x² - 3x = 2.

"X" is like an edgier version of "Q". Oh, your letter is a circle with a little diagonal line through it and it's used for sounds that other letters already make? Here's a bigger diagonal line with another diagonal line through it and it's sometimes pronounced as a freakin' "Z". Also, it hangs out with the weird letters in the back of the alphabet, not those respectable letters like "R", "S", and "T".

6:42 actually Old Spanish did have a letter to represent the SH sound, it was the letter X! this is because the sequence KS from Latin turned into a sh sound in Old Spanish (like in "laxius" > "lexos"), which still existed in the 1500s and 1600s, but which shifted to a H sound in modern Spanish ("lexos" > "lejos"). It is now spelled as J because the Old Spanish letter J represented a ZH sound (similar to the SI in vision), but this sound also became H in modern Spanish so there was no point in keeping the distinction in writing, and since J was more common all of the X got replaced with J, except in a few words like México, which is pronounced as tho it was written Méjico. In Portuguese and Catalan, which are both closely related to Spanish, the letter X is still pronounced as the SH sound, tho now Portuguese prefers spelling it as CH for similar reasons to the ones that led Spanish to prefer J for the H sound Now this is all really simplified and dumbed down to the best of my abilities but there's still a whole lot of stuff that could be explained in more detail. My point is just that Spanish already had the X letter for the Arabic SH sound, so there's no need to say they borrowed Greek Chi, which adds more force to the hypothesis by making it simpler

In algebra, my thought was just as `a` is the first letter of the `abc` trifecta that starts the alphabet, and `x` is the first letter of the `xyz` trifecta that ends the alphabet, then `a` and `x` are the first choices for constants and variables, respectively.

X it's also one of the only letters that you can use as something other than a letter. Like when you cross out something on paper.

I think it's important to include the shape of X, it's a very satisfying & easy thing to draw. Like X is more fun to draw than +, that's a little weird.

You spoke the logic and philosophy of X in the first few minutes of this very episode. It is, it’s very scarcity in language, called it into used in mathematics. What better integer placeholder to use than something that is so uncommonly used, it cannot be confused with any other use? Philosophy led the way X. It’s scarcity made it the perfect place holder for unknown because you cannot be confused for anything else.

The Greek letter for x is Ξ (capital) or ξ, lower case, not Χ. It is pronounced ksee. Chi is a fricative, like the ch in German Bach. The x in old Spanish was in fact pronounced like English sh, so such a translation from Arabic would have made perfect sense.

Additionally, X is used to indicate negation or important things (as in "X marks the spot"). By the way, in Mexican Spanish, calling something or someone X ("equis") means that it is irrelevant or indifferent (like saying "meh" or "whatever").

Interesting video. I knew pieces of this, but it's nice to see it all put together. Minor critique though. I'm studying Arabic, and I noticed that شيء is incorrectly written left to right at 6:20.

Fun fact, today the sound of "X" in the modern Greek alphabet is written like "Ξ", which is almost identical to the ancient Phoenician one at 1:29!

I remember, that in first grade, we learned how to write all the letters of the alphabet, but they kinda forgot to teach us how to write x (or I was not there or idk). So for me it was the unknown letter, making it a natural transition to an unknown value in math later in school.

You forgot the treasure maps, where the X marks the spot you should dig, to find the hidden treasure. My fav word with X is Axolotl!

The "we dont even need it" intro fit well with Xtwitter.

And now it's not uncommon to use symbols from, like, three different writing systems, which I think is cool because those symbols have their own meaning based on context.

This is so well timed with back school 😂 I’ve been solving for X a lot this week helping my 8th grader with homework.

I feel that Elon Musk if secretly behind the creation of the video, lurking in the shadows....🤣

I think it has more to do with the fact that it's not useful, so it's easier to use without confusing it with existing abbreviations and acronyms and such. And more importantly, it's simple and visually striking, probably more so than any other letter, and easy to write.

I love X so much that my most searched term on my browser is triple X

This sort of video is such a treat to watch at early morning being all comfy as it also pacifies my heart as I am learning something 😅

By "WE" you mean Elon Musk? 🤣🤣🤣🤣

2:35 oh no! The bottom equation shohld have a + as the second symbol, not =.

X is also completely balanced in all 4 directions and is the mirror image of itself in all ways. This makes it incredibly esthetically pleasing in my opinion.

TBH,the best channel in english!keep up the good work smart Joe❤

2:15 I think this problem doesn't have a positive solution. The second one has size of more than 5. Therefore, its area is more than 25. Therefore, the total area is more than 25. However, there is a solution if you allow the plots to be points

Well, it’s because it’s just such an X-cellent letter, that’s just why we simply love the letter X. 🙂

OMG! What a nice video! I've learned a lot. The history of the X is very interesting and quirky!

Be Smart is remarkable. Thank you very much. I love you and I appreciate your hard work and effort you put into your videos in order to describe things as clearly and precisely as possible. ❤😊

The story of sound preservation from Arabic might make more sense if the translators were Portuguese rather than Spanish. The most common sound for X in Portuguese is indeed "sh", but it may also sound like "s", "z", or "ks".

"You're blackmailing me!?!" "Blackmail is such an ugly word. I prefer 'extortion'. The X makes it sound cool."

Most people: *watches video out of curiosity* Me: THE CONTINUOUS SEARCH OF A PERSON THAT ADDED LETTERS TO MATH SHALL BEGIN

So adorable information...Even i can't speak english but i could understand you easly.Thanks for this clear english and information and you gained a new subscriber )

"X"... A most ancient letter. Some say "kye," but the meaning is the same. Death... A letter that spells endings.

8:13 A French printer wouldn't have a load of x's because it is rare, they would have a load of the most popular letters because they are popular. If, say, only 1% of letters in French were x then the printer would only have 1% of x's in stock. Given a letter with 4% frequency they would have 4 times as many.

Very good video! It has a lot of information.

X has a plosive sound which makes it pretty satisfying. That's also why the f word is used so much. It also looks pretty cool. So it's a case where the stars aligned

Is this a prelude to us staging an intervention for Elon Musk?

The Pokémon franchise seems quite obsessed with X too. In the TCG you have Pokémon EX and GX, and then you have side/mobile games like Pokémon XD, Pokémon Masters EX, and Pokkén Tournament DX. Oh, and for those old enough to remember, the Japanese advertising for the second Pokémon movie - the one featuring Lugia - used an “X” motif to refer to that particular Pokémon as well. Apple seems to be another huge fan of the letter X: not only did you have MacOS X, you also had the iPhone X, the iPhone XS, and the iPhone XR. There’s also Final Cut Pro X, and there used to be a QuickTime X as well. I’m sure other people can find a ton of other non-elongated muskrat examples of our obsession with the letter X as well. 👀

'X is everywhere' Almost every other writing system: Whats that?

3:01 I don't know about Brahmagupta, but as a child, my father told me how ancient mathematicians used seeds of plants to refer to unknowns in equations. Upto this day, the term for algebra in Hindi is "बीजगणित" [beejganit], where "beej" means "seed" and "ganit" means "mathematics".

0:28 I feel that Q is just as unnecessary. The Q sound is already represented by K just as Qu is with Kw. There's no need for the letter Q. Getting with of Q and X brings the alphabet to 24 letters, a multiple of the venerated 12.

10:03 well it's rather a CROSS instead of the letter X ...

Really fun video! Thanks 🙂

Mathematician here! Love love love this video 💕

Incredible, I am still an engineer student but have never learn a more clear way on the origin of algebra and how that leads to calculus with the importance of functions. Great work

I think it has a bit to do with how simple and elegant the letter is. X is very simple and district. Unlike p for example that is curved and also is similar to q d and b. And that matters when you're trying to grab someone attention, such as with a logo. That is not to say other letters can not have the same effect. The Q in game Quake is very iconic. But it does not look like your regular Q. While most uses of X do very much look like a X.

Excellent presentation,expert Joe Hanson ❤

"Apps too i guess" is almost as good as "the social media site formally known as Twitter"

I think it's strange that the English alphabet has two letters that make the same sound as a combination of two other consonants, but not even commonly occurring consonant pairs. So not only do these letters not make their own sound, they don't even represent commonly used sound combinations, so it's not like they justify their place in the alphabet as useful shorthand. Meanwhile, English has some commonly used sounds that don't have their own letters to represent them.

4:30 alkhuawrizmi used letters in math. Most famously س

tbh the thing i'm most amazed from this video is the fact that when you look at it relatively the graph thingy is suprisingly new

I never ever heard that anyone normal is obsessed with a letter

I won't look or search trough hundreds of comments.. but 0:43 ... x = 2a , not 3a.. 3rd row should be x + x - x = 8a - 2a - 3a - a ... buuuut I have not watched any further yet, so maybe that is on purpose :D

0:18 the ABCs should follow this

As possibly histories least subtle international man of mystery I'm flattered to be granted such a prestigious title

thank you, I appreciate this!

I wouldn't say "we" as in humanity, and more so elon musk and his fanboys

5:37 Literally coding today

Great video 😊

What a great video to watch while procrastinating on my calculus homework!

By "we" you mean Weirdon musk?

As a French I totally validate to the scene with the French printers.

Love this video. X

It makes me want to cry that after half a year of meds I'm barely able to keep up with your voiceover. ×

0:54 theories as to y?

the background music at 4:20 has a terrible 'semi-backing-up' sound in it that's very subtle and I didn't like it lol

Even Mutants are mysterious characters in the Marvel comicbooks universe so that's why comicbook creator Stan "The Man" Lee used letter X symbol or emblem on how Mysterious all the Mutants are.

Great video

I think names that start with X is pretty cool

5:52 there's a pi in the wrinkles on your forehead

lol @ "Only if it'll shut you up, Xavier" 😁

X finds me. I chose the name Gen X to help people determine my age on social media. Then I ended up getting a Lincoln MKX The MKX is actually a Lincoln Mark 10 but they replaced the 10 with the Roman numeral X. It's part of my life now.

Thanks for that video. By the way, at 11:26 you pronounced _Descartes_ right by mistake lmao ^^

"we" are not.

This is my favorite one yet!

"Every mathematician uses different symbols and no one could read anyone else's work" - Excellent summary of applied mathematics.

I always find it fascinating how Pi became 3.1415..., because it was originally meant to be a generic variable in the equation and it just caught on. It wasn't even used for the radius initially, it was used for the circumference.

3:58 agreed.

Minor complaint and it really is minor. At 6:21 the word "Shey" is written from left to right instead of right to left "شيء" and the letters are not connecting. Probably a mistake in the editing program as I've had some programs just completely disregard Arabic and ignore it's writing system.

"Solve x" must be final boss in math game if there exists

In my eyes it seems likely that the same sort of thing happened as what you feel when naming variables in programming. You want to make absolutely sure that you don’t repeat yourself on accident so you pick something you feel is „secluded“, „rare“ or „far away“ from the other variables you named.

I don't know if there's anything to this but X is perhaps *the* most kiki (as opposed to bouba) letter in the alphabet which helps to give it a certain edge and even somewhat of an aesthetic in and of itself?

Great Video! One note, in Arabic, we don't have consonants linking together much, because of the different ways to spell each letter. So the guy's name is Al Kha-wa-riz-mi

One characteristic of the letter X that was not considered is the plasticity of it. X is easy to spot and to write on paper, which is the main point imho.

Hey Joe -those apparently hip-hop loving retirees you showed at 0:11 are clearly Boomers, not NOT Generation X!! (I can’t believe you millennials view us Gen X’ers as if we are nursing home residents!).

x was chosen due to its relative disuse in regular diction. x stands out like a sore thumb amongst common words, such as a lengthy explanation of a mathematical theory. this allows the variable to avoid conflation or confusion with other symbols on the page.

I was just talking about this very topic last week

X marks the spot? Nah, X spots the marks

Not us, just Elon Musk

Watching this video made me realise that I assumed writing math like we do with all of the symbols was a universal-always-have-been-that-way kind of thing... But of course it is such a recent thing and of course people used to just write them out in words and it all makes such sense if I just thought about for one second, but I never did because I assume the world is never-changing and permanent...

the quality of his content is top notch

Thank you...for this video