Where did the letter x come from?

The letter "X" originated from the Phoenician letter "samekh," which represented a voiceless fricative sound. It was later adopted by the Greeks as "chi" (Χ), representing a "k" sound. The Romans then took the Greek letter, transforming it into the "X" we use today, which represents various sounds in different languages. Over time, "X" has come to symbolize various concepts, such as multiplication in mathematics and the unknown in algebra.