# Early proofs of Leibniz's formula

Wikipedia attributes Leibniz's formula to Madhava of Sangamagrama, James Gregory and Gottfried Leibniz. But what were their proofs?

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–  Alex Nov 12 '12 at 3:14
sorry about the format –  Alex Nov 12 '12 at 3:15
@ Alex - I don't see a proof in the article on Madhava of Sangamagrama. Thanks for the other reference. I wish we had a reference that tied Gregory's proof down to a specific historical source. –  Jonah Sinick Nov 12 '12 at 3:23
en.wikipedia.org/wiki/… –  Alex Nov 12 '12 at 3:26
A good reference for this question is Ranjan Roy: The Discovery of the Series Formula for $\pi$ by Leibniz, Gregory and Nilakantha. Mathematics Magazine, Vol. 63, No. 5, December 1990, pp. 291-306. The article is reprinted in Berggren et al.: Pi: A Source Book.