F(x)

f(x) ( /ˌɛf ˈɛks/; Korean: 에프엑스) 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. The f stands for flower and the x represents the female's double x chromosome. 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.

2011–present: First album Pinocchio and Hot Summer

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 the first half of the year.
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",[9] written by Thomas Troelsen and Remee), their OST song for "Paradise Ranch" and digital singles "Chu" and "La Cha Ta."
In August 2011, f(x) released an OST called "Garagabana" for the online game "Bust-a-Move".
On December 13, 2011, f(x) released and English song entitled "1, 2, 3" as part of the album 2011 Winter SMTown – The Warmest Gift

Members

Stage name		Birth name		Date of birth
Romanized	Hangul	Romanized	Hangul/Hanzi
Victoria	빅토리아	Song Qian	송천/宋茜	(1987-02-02) February 2, 1987 (age 25)
Amber	엠버	Amber Josephine Liu	류일운/劉逸雲	(1992-09-18) September 18, 1992 (age 19)
Luna	루나	Park Sun-Young	박선영/朴善怜	(1993-08-12) August 12, 1993 (age 18)
Sulli	설리	Choi Jin-Ri	최진리/崔雪莉	(1994-03-29) March 29, 1994 (age 18)
Krystal	크리스탈	Krystal Jung, Jung Soo-Jung	정수정/鄭秀晶	(1994-10-24) October 24, 1994 (age 17)