Episode X

Straight from the 1990s to your faaaaaaace! Why do we solve for X? One theory: x traces back to the Arabic word for “thing,” or šay’. In ancient texts, such as Al-Jabr, a manuscript written in Baghdad in 820 A.D. that established the rules of what became algebra, mathematical variables were called “things” or šay’. When Al-Jabr was later translated into Old Spanish, the word šay’ was written as “xei.” This soon came to be abbreviated as x. Theory 2: the Greek word for unknown, xenos, also begins with x, and the convention could simply have been born of an abbreviation for xenos as chi, X. Renee Descartes used the convention of lowercase letters at the beginning of the alphabet for known quantities and those at the end of the alphabet for unknown quantities. One story goes that it was Descartes’ printer who suggested x be the principle unknown in La Géométrie because it was the letter least used and so had the most available. Xs and Os to Kay, Mark, Carrington, and Paul.