Triangle (officially published and stylized as the symbol ⊿, pronounced Triangle (トライアングル^?, Toraianguru)) is the title of the second original studio album (third overall) of Japanese girl group Perfume. Triangle was officially announced at Perfume's Disco!Disco!Disco! concert, and was released on July 8, 2009 as a CD-only version and limited edition CD+DVD version, which featured promotional music videos and live performances. The album was recently released on iTunes worldwide along with the other, previously unavailable, albums of their career.

Triangle was released seven weeks after Yasutaka Nakata's effort with Meg, Beautiful. Despite selling lower than their first original album, Game, Triangle was certified platinum by RIAJ for selling over 250,000 copies.

The first track, "Take off" is a less than one minute instrumental. It plays the role as the introduction of the whole album and leads to the second song, "love the world, the seventh major single. "Dream Fighter" is the eighth major single. The next song "edge (⊿-mix)" is the b-side song from the single "love the world". This mix is over eight minutes and a little longer than the extended mix in the single. "NIGHT FLIGHT" is an 80's technopop-like song, which features a chopper bass. It was used in ads for Morinaga Milk's Pino Airlines campaign. Like the concept of the ads, the lyrics compare love with airplane flying. "Kiss and Music" is an R&B and hip hop influenced song. "Zero Gravity" is an electronic house song which features an electric piano. "I Still Love U" is an 80's Japanese idol R&B-pop-like song. It received an exclusive video, available on the limited edition DVD. "The best thing" is the ninth track of the album which was described as Yasutaka Nakata's (producer of Perfume) signature sound with arpeggios and a house track. "Speed of Sound" is a Latin trance-house-like song which has few words (similar to Meg's song Make Love). "One Room Disco" is the ninth major single. The finale is "Negai (Album-mix)". The song originally was a low-tempo ballad song in the b-side of "Dream Fighter", but in the album, the song features more strings, and is arranged to be more orchestral.

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