Pai

alt=A diagram of a circle, with the width labeled as diameter, and the perimeter labeled as circumference|thumb|right|350px|Uwiano wa urefu wa mzingo na ule wa kipenyo ni 3 na kitu. Uwiano kamili unaitwa π, pai.

Pai (jina la herufi ya Kigiriki π) ni namba ya duara kwa maana ya uwiano wa urefu wa mzingo na ule wa kipenyo.

Jinsi ilivyo kawaida kwa herufi mbalimbali za Kigiriki, pai pia inatumika kama kifupisho kwa ajili ya maarifa na dhana za hesabu na fisikia. 

Imejulikana hasa kama namba ya duara. Ikiandikwa inanaza 3.141592653589793238462643... lakini haiwezi kuandikwa kamili kwa kuongeza tarakimu baada ya nukta maana hakuna mwisho. Namba za aina hii zisizo sehemu ya namba nyingine au ambazo haziwezi kuonyeshwa kuwa wianisho safi baina namba kamili huitwa namba zisizowiana.

Chamkano cha 22/7 ni karibu zaidi na pai na 355/113 ni karibu zaidi tena.

Wanahisabati duniani husheherekea sikukuu ya pai tarehe 14 Machi au pia 22 Julai.

 Marejeo 

  English translation by Catriona and David Lischka.






 , English translation by Stephen Wilson.




 . [http://www.jstor.org/discover/10.2307/3029284 issue 3 Jan/Feb], issue 4 Mar/Apr, issue 5 May/Jun

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