Pi
Lamba π ( /p aɪ / ; da aka rubuta a matsayin " pi ") ma'auni ne na lissafin lissafi wanda shine rabon da'irar da'irar zuwa diamita, kusan daidai da 3.14159. Lambar π tana bayyana a cikin dabaru da yawa a cikin ilimin lissafi da kimiyyar lissafi . Lamba ce mara hankali, ma'ana cewa ba za a iya bayyana shi daidai a matsayin rabon lambobi biyu ba, kodayake ana amfani da juzu'i kamar 22/7 don kimanta shi . Saboda haka, wakilcin sa na goma ba ya ƙarewa, kuma ba ya shiga tsarin maimaitawa na dindindin . Lamba ce mai wuce gona da iri, ma'ana cewa ba zai iya zama mafita ga daidaiton da ya ƙunshi jimla kawai, samfura, iko, da lambobi ba. Maɗaukakin π yana nuna cewa ba zai yuwu a warware ƙalubalen da aka daɗe ba na murƙushe da'irar tare da kamfas da madaidaiciya . Da alama ana rarraba lambobi goma sha ɗaya na π,  amma ba a sami tabbacin wannan zato ba.

Tsawon shekaru dubbai, masu ilimin lissafi sun yi ƙoƙarin faɗaɗa fahimtar π, wani lokaci ta hanyar ƙididdige ƙimarsa zuwa madaidaicin matsayi. Wayewa na da, da suka haɗa da Masarawa da Babila, sun buƙaci daidaitattun ƙididdiga na π don ƙididdiga masu amfani. Kusan 250 BC, masanin lissafi na Girka Archimedes ya ƙirƙiri algorithm don kimanta π tare da daidaito na sabani. A karni na 5 miladiyya, masana lissafin kasar Sin sun kai kimanin π zuwa lambobi bakwai, yayin da masu ilmin lissafi na Indiya suka yi kimamin lambobi biyar, dukkansu suna amfani da fasahar geometric. Ƙididdigar ƙididdiga ta farko don π, bisa jerin ƙididdiga marasa iyaka, an gano shi shekaru dubu daga baya.[1][2] Sanin farkon amfani da harafin Helenanci π don wakiltar rabon da'irar da'ira zuwa diamita shi ne na masanin lissafin Welsh William Jones a 1706.[1]
Shafuka masu fassarorin da ba'a duba ba