(1) In ancient times, interchangeable words were commonly used, and "yuan" was connected with "source". Solving equations is actually tracing back to the source. This explanation comes from Baidu.

(2) "Yuan" is also a variable. A unary equation contains one variable, and a binary equation contains two variables. This explanation also comes from Baidu.

(3) David, the founder of symbolic algebra, uses vowels A, E and I to represent the unknown, so the unknown is called "yuan".

(4) Yuan is a quantifier, similar to Yuan in One Qian Yuan and Two Qian Yuan.

(5) "Yuan" is a mathematical term coined by Xu Guangqi when he translated "Elements of Geometry" in Ming Dynasty.

(6) "Yuan" is a mathematical term introduced into China from Japan.

(7) "Yuan" is just a mathematical term established by people.

None of the above explanations is the real reason why the unknown is called "yuan"

In fact, the use of the word "Yuan" to express the unknown originated from the art of Heaven in the Song and Yuan Dynasties in China. The so-called Tiandao method is to "make Tianyuan a certain" when solving algebraic problems, then establish an equation according to the conditions of the problem, and finally get an equation by shifting terms and merging similar terms. "Let Tianyuan be someone" is now "Let someone be X".

In today's English, the noun corresponding to "unknown" is "unknown", which is generally represented by X, but different countries or regions have different names or representations of historical unknowns.

Why do you often use X to represent the unknown today? There are many explanations in academic circles, among which Descartes' theory of invention is widely recognized, and Kayoli believes that there is no basis for other explanations except Descartes' theory of invention.

Descartes said: Descartes, one of the inventors of analytic geometry, used the first letter of the alphabet, such as A, B and C, to represent known numbers, and the last letter, such as X, Y and Z, to represent unknown numbers. But in the second half of the book, X appears more frequently than Y and Z. There is a story that when geometry was still typesetting, the printer found that Y and Z were not enough because they were used more frequently than X. He asked Descartes, is there any difference in the meaning of using different letters in X, Y and Z to represent the unknowns in the equation? Descartes replied: it makes no difference to use any of the three. Therefore, the printer can safely and frequently use the X printer.