f(x) (Korean: 에프엑스; pronounced /ˌɛf ˈɛks/) 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, and when input with different ‘x’, there can be many different outcomes. f(x) strives to be the kind of girl group that can change and adapt to many situations. The group members have also been nicknamed “function girls”. The group made their debut on September 1, 2009 with release of a digital single “La Cha Ta” (stylized as “LA chA TA”). The quintet consists of Victoria, Amber, Luna, Sulli and Krystal.
(L-R)Krystal, Sulli, Victoria, Amber & Luna
|Origin||Seoul, South Korea|
|Genres||Pop, rock, electro-pop|
|Labels||S.M. Entertainment (South Korea)
|Associated acts||SM Town|
 Pre-debut history
Krystal Jung was first spotted by SM Entertainment in 2000 on a family visit to Korea, 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”. Victoria was spotted by a S.M. Entertainment’s agent at a Beijing dance competition, and later joined the company. Two months later, Amber was cast through SM’s Global Auditions in Los Angeles, California, where she was one of two people (one male) selected to be trainees.
 2009: Debut, first single album and collaborations
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 their first single album, Chu~♡, consisting of 3 songs.
 2010: First mini-album, Amber’s hiatus, and SMTown World Tour
On January 2, the group released the Chinese track, “Lollipop”, a slick derivitive of the famous 1958 classic “Lollipop” – written by Julius Dixson and Beverly Ross, 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 Tokyo, Shanghai, Los Angeles and Paris (2011) 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.
 2011–present: First album Pinocchio and Hot Summer
The first teaser photo for their full-length album entitled Pinocchio was released on April 7, 2011 at the f(x) official website. The MV teaser for the lead single, “Pinocchio (Danger)” (a remake of Kristine Elezaj‘s “Razor”), was released on April 15, 2011. The album was released on April 20, 2011 and the group held their first comeback stage through KBS’s Music Bank on April 22, 2011.
The group have achieved 8-wins with “Pinocchio (Danger)” from the music shows, namely M! Countdown, Music Bank and Inkigayo.
On June 8, it was announced that f(x) would be releasing their repackaged album of Pinocchio, titled “Hot Summer”, on the 14th. It included all 10 songs from their first album and new track “Hot Summer” (a remake of Monrose‘s “Hot Summer”, written by Thomas Troelsen and Remee), their OST song for “Paradise Ranch” and digital singles “Chu” and “La Cha Ta.”
As of 2011, f(x) is considered one of the “five in the middle” in the South Korean girl-band scene, alongside T-ara, After School, SISTAR, and Brown Eyed Girls — after the “strong four” consisting of Girls’ Generation, 2NE1, Miss A, and Kara.