The X Factor

01 Dec 2017

Why is letter “X” is the default choice when you need to represent an unknown variable in Algebra, out of the 26 letters in the alphabet? To find out, let’s delve into the origins of Algebra.  

The X Factor
Understanding algebra

Algebra was invented by Arabian mathematicians in the 800s. The word “Algebra” comes from the Arabic word “al-jabr”, which means “restoration.” In the 9th century, a Persian mathematician named Muhammad ibn Musa al-Khwarizmi translated many ancient Indian and Greek mathematical works, including the seminal “Addition and Subtraction after the Method of the Indians”, and compiled them into the mathematical bible of its time. Thanks to this feat, he became known as the Father of Algebra.  

Back then, mathematicians used the Arabic word “šhay”, which means “thing”, to represent the unknown that they wanted to find, much like the way modern mathematicians use “X”.

The X Factor
Spain, where an early concept of “x” was birthed.

In the 11th century, when the concept of Algebra reached Spain, Spaniards found the word “šhay” difficult to pronounce. Thus, Spanish scholars replaced the “sh” sound with the Greek “ch” sound, which is represented by the Greek “chi”. Written as χ, eventually, this morphed into the modern “X”  

That’s how “X” became the default representation of an unknown variable in Algebra!

The X Factor
Algebra can be confusing at times.

Fun facts about the letter “X”:

  1. Words that begin with “X” are relatively rare in English. There are only about 120 proper nouns in English that start with “X” – i.e. names of places, people and events. Aside from these, there are only about 400 words beginning with “X”. An example is “xanthodontous”, which is an adjective that means “having yellow teeth”.
  2. Many words that begin with “X” have Greek origins.
  3. In modern English, the letter “X” is one of the least used letters. Other rarely used letters include “Q” and “Z”



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