X

Why is the letter "X" used for the unknown in algebra?

It was Renee Descartes, the 17th century philosopher and mathematician, who began the use of letters at the end of the alphabet to represent unknown quantities, with X as the choice for the first unknown. Why X and not Y or Z? He never gave an official reason, but most scholars agree that the widespread adoption of the X is, in spirit, ease and simple. One could write the letter X quickly and it was more likely to be legible than other letters.

(Source: "How do astronausts scratch an itch?" by David Feldman)

Galing yan dito.

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