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Dong Youcheng
Short-lived Qing mathematician from Yanghu who derived the infinite series for trigonometric functions transmitted by the Jesuit Jartoux
In a calculation room, a wide table holds a board of black and yellow counting rods laid in neat bundles, beside an abacus, a ruler and a sheet with a circle divided into equal parts; one person sits at a far desk with their back turned, and terraced fields lie outside.
Also known as Zi Fangli
- Roles
- Mathematician
Dong Youcheng, courtesy name Fangli, came from Yanghu in Jiangsu and studied as a youth with his elder brother Dong Jicheng, taking up geography, calendar science and mathematics. He passed the provincial examination in 1818 but did not succeed at the metropolitan level. Finding that three infinite series for pi and for the sine and versed sine, brought to China by the French Jesuit Pierre Jartoux, had circulated without derivations, he wrote a three-chapter illustrated explanation of circle division by continued proportions to derive them. He also wrote on sums of piled objects (finite series), the circumference of an ellipse, and spherical triangles. He died in 1823 at only thirty-three, and his brother published his writings as the Posthumous Works of Dong Fangli.
Life and times
Dates 1791 CE–1823 CE