Person: Landen, John
John Landen was an English amateur mathematician who wrote on mechanics, summation of series and elliptic functions.
Mathematical Profile (Excerpt):
 John trained to become a surveyor and practised that occupation in Peterborough from 1740 to 1762.
 Landen was never a professional mathematician and his interest in mathematics was for him a leisure activity.
 Lacroix discussed this work in Traité Du calcul différentiel where he stated that Landen was the first to present calculus in a purely algebraic setting.
 Landen's work appeared as A Short Discourse Concerning the Residual Analysis published in 1758 and, in a more complete form, in Residual analysis which was published in 1764.
 His ideas on this topic were later taken up by Lagrange although he describes Landen's contribution as an unsophisticated early attempt.
 Landen investigated the dilogarithm in 1760, about the same time as Euler, and introduced the trilogarithm.
 Landen wrote on dynamics, summation of series and an important transformation giving a relation between elliptic functions.
 Naturally, Landen's language is that of his time, in terms of fluents and fluxions, and his arguments are not rigorous in the modern sense.
 Applications of this result appeared in Landen's Mathematical memoirs of 1780.
Born 23 January 1719, Peakirk (near Peterborough), England. Died 15 January 1790, Milton (near Peterborough), England.
View full biography at MacTutor
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Origin England
Thank you to the contributors under CC BYSA 4.0!
 Github:

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 @JJO'Connor
 @EFRobertson
References
Adapted from other CC BYSA 4.0 Sources:
 O’Connor, John J; Robertson, Edmund F: MacTutor History of Mathematics Archive