f(x)

f(x) (Korean: ????) is a five member South Korean girl group formed by SM Entertainment in 2009. 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 ??? (LA chA TA). The quintet consists of ???? (Victoria), ?? (Amber), ?? (Luna), ?? (Sulli) and ???? (Krystal).

Krystal Jung was first spotted by SM Entertainment in 2000, which earned her a small role in a short segment of Shinhwa's "Wedding March" music video. Sulli Choi first debuted as a child actress in 2005 when she was selected to play young Princess Sun-hwa in the SBS television drama, The Ballad of Seo-dong. In 2006, SM Entertainment recruited Luna after seeing her performing on SBS's television program, "Truth Game". In September 2007, SM Entertainment recruited Victoria Song. A month later, Amber was cast from an audition in Los Angeles, California.

SM first released a teaser preview of the group via YouTube on August 24, introducing them as "Asia's Pop Dance Group." For five days, SM individually released information through news portals and posted pictures of each member on SM Town's official website, starting with Korean member Sulli on August 26, Taiwanese-American member Amber on August 27, Korean-American member Krystal on August 28, Korean member Luna on August 29, and lastly the Chinese member Victoria on August 30.

On September 1, the group's first single "La Cha Ta" (stylized as "LA chA TA") was digitally released. Following their first performance at the Samseong-dong Fashion Center on September 2, the music video was screened and released online the next day. The group's first broadcast performance of "La Cha Ta" was held at MBC's music show Show! Music Core on September 5.

On October 7, the group also released the electro-pop version of the digital single, "Chocolate Love", alongside their label mate Girls' Generation. The single was released for the promotion of the 4th edition Blacklabel series of LG CYON phone, LG Chocolate (BL40).

On November 9, f(x) released its first single album, Chu~?, consisting of 3 songs.

On December 19 and 20, f(x) appeared as special guests on Into the New World concert of their label-mate girl group, Girls' Generation, in Olympic Fencing Gymnasium.

On January 2, the group released the Chinese track, "Lollipop", for which they collaborated with the Chinese boy band, M.I.C, to promote the LG Cyon phone. The music video was digitally released on January 12, 2010.

On February 27 and 28, the group appeared once again as special guests on Into the New World concert in Olympic Fencing Gymnasium.

On May 4, f(x) released their first mini-album, Nu ABO, consisting of 6 tracks. The lead single, "Nu ABO", topped online music portal charts Monkey3, Dosirak and Bugs. The song also made it to the Gaon Chart weekly number-one singles. The music video for the song was released on May 6. The group made their live comebacks on KBS's Music Bank on May 7, MBC's Music Core on May 8 and SBS's Inkigayo on May 9.

On July 17, the group started performing their next promotional single, "Mr. Boogie", from their mini-album, Nu ABO. They had their first performance for the song on MBC's Music Core.

f(x) also participated in the SMTown Live '10 World Tour alongside their label-mates on August 21 at Seoul Jamsil Olympic Stadium. They also performed in Shanghai and Los Angeles on later dates. This marks the first time f(x) and their fellow label-mate groups performed outside of Asia.

On November 24, 2010, Avex Entertainment, as well as SM Entertainment Japan, released a statement about the renewal of contracts of SM artists signed to Avex. It stated that f(x) is now signed to Avex, and its albums will be released under the said label in Japan, Taiwan, China and Hong Kong.

It was announced by SM Entertainment that Amber returned from USA after a long leave since June 2010 and that f(x) are planning to release a studio album in February 2011.

f(x) finally released their first album "???? (Pinocchio)" on April 20, 2011. The album's lead single "(????) Danger" immediately went to #1 and stayed at the top of various online charts such as Melon. On April 29th f(x) received their first k-chart award on Music Bank.