f(x)

f(x) is a four-member (originally five-member) South Korean girl group formed by SM Entertainment active from 2009 to 2016. The name is a play on the mathematical notation for function, with "f" signifying "flower" and "x" representing the female's double X chromosome. The group made their debut on September 1, 2009 with release of a digital single "라차타 (LA chA TA)". The group was initially composed of 宋茜 (Victoria), 엠버 (Amber/Amber Liu), 루나 (Luna), 설리 (Sulli) and 크리스탈 (Krystal).