I realize that X and Y are reasonably popular terms as soon as wanting to use a placeholder because that an unknown English or mathematics term. What is the origin of this term, and why was it X and Y; why not the other letters?

They came to be popular since of René Descartes’ usage in his La Géométrie. The letter at the end of the alphabet are preferred as the variables, if those in ~ the start are constants. There is speculation about why this could have to be done. It is likely to enable the largest number of sequential letter without overlap in between the two sets.

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Why x came to be the most common is unknown. Some sources attempt to draw a heat from the Arabic word because that unknown v the Greek letter chi (which resembles a funding X), yet the cases are unsubstantiated (Arabic being the source of our numerals and Greek gift the typical letter collection for variables).

The link from math to usual speech is likely simply a basic repurposing of recognized concepts.

$\begingroup$ It appears the obvious selection as, X is what you do your mark with. However when's that from, cuneiform? $\endgroup$
$\begingroup$ five possibly. As crossed lines space the simplest way to mark an exact point top top a map, this was also likely used far before cuneiform, even. However, the usage of “x” in the place of an arbitrarily or unknown didn’t rise prior to Descartes popularized it. $\endgroup$
See Earliest provides of math symbols, i m sorry quotesF. Cajori, A history of mathematical Notations, 2 volumes (1928-29)

The usage of z, y, x ... to stand for unknowns is because of René Descartes, in his La géometrie (1637). Without comment, he introduces the usage of the very first letters of the alphabet to denote known quantities and the usage of the last letter to signify unknown quantities.

$\begingroup$ It's fascinating how much influence one person have the right to have. Ns wonder what René would say this particular day if he witnessed x as variable name splattered all over classrooms worldwide, journals, whiteboards, labs, computer system code... $\endgroup$
Here is the original source : René Descartes, La Géométrie (1637), I, page 299, because that $a,b$ provided to denote parameters.

And view I, page 301 because that $z$ and I, web page 303 for $x,y$ respectively, used to describe an unknown quantity.

Letters was currently used by François Viète (but the use of alphabet variables to represent magnitudes is because of euclidean geometry).

See In artem analyticem isagoge (1591), Rule III :

Sunto duae magnitudines $A$ & $B$.

Oportet $A \dfrac \text plano B$ addere $Z$ .

But obviously the success of Descartes" "new geometry" describes the success the the new algebraic notation.

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