# Unraveling the Mystique of the Letter X – From an Ancient Enigma to a Modern Symbol

Even though X is one of the least-used letters in the English alphabet, it permeates American culture, from Stan Lee’s iconic X-Men superheroes to the enigmatic allure of the TV series *The X-Files*. X is a symbol of the unknown – a cipher for a mystery that casts an irresistible spell.

## X Is a Ubiquitous Symbol

This fascination with X is visible in contemporary figures like Elon Musk, who has harnessed the captivating power of the letter with ventures like SpaceX, the audacious Tesla Model X, and even Twitter’s transformation into the enigmatic X. Despite that, most people primarily recall X from math class, where it serves as a versatile variable representing an elusive quantity. But why was that symbol chosen for this role, and where did this originate?

It is rather challenging for historians of mathematics to pinpoint definitively how X assumed its role in modern algebra. In ancient times, algebra was conveyed through verbal narratives, with mathematical problems and solutions woven into stories much like today’s elementary school word problems. Ancient civilizations such as the Egyptians and Babylonians employed different terms to denote unknowns, often tied to geometry even when problems weren’t geometric in nature.

## René Descartes Standardized the Mathematical X

As mathematical knowledge developed independently across diverse cultures and languages, some symbolic notations began to emerge. Yet, full standardization was hindered by communication limitations. The transition toward symbolic notation was gradual. Notable mathematicians like Diophantus of Alexandria used archaic Greek letters as symbols for the unknown. Indian mathematicians, including Brahmagupta, contributed to the evolution of modern decimal symbols and quadratic equations. Islamic scholars preserved and translated mathematical knowledge, significantly impacting global mathematics.

The genesis of X as the unknown in algebra can be traced back to these Islamic roots. A theory posits that the Arabic word ‘al-shayun,’ meaning ‘something,’ was shortened to its first ‘sh’ sound. Spanish translators, faced with the absence of a letter for this sound, represented it with the Greek letter ‘χ,’ which later became the Latin ‘x.’ However, the Spanish alphabet already included X and early Catalan exhibited various pronunciations, some akin to the modern ‘sh.’ Vestiges of this pronunciation remain in Portuguese, Mexican Spanish, and place names. This suggests that X could have been employed without necessitating the intermediary step of the Greek ‘χ.’

The most plausible explanation attributes the modern use of X to the influential French scholar René Descartes. In 1637, he introduced analytic geometry, employing letters for constants and variables, with the first few letters of the alphabet for constants and the last in reverse order for variables.

Though the origins of X in algebra remain uncertain, some instances stand clear. German physicist Wilhelm Röntgen’s discovery of X-rays in 1895 kindles the mystique of X. As for Elon Musk’s affinity for X, explanations range from his status as a Generation X representative to the historical association of X with mystery.