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Qin Jiushao
Southern Song official and mathematician whose Mathematical Treatise in Nine Sections (1247) solved systems of congruences and higher-degree equations
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 Daogu
Qin Jiushao, courtesy name Daogu, came from Anyue in Puzhou, though he called himself a man of Lu; his father Qin Jiyou served as prefect of Bazhou and in the Palace Library. As a youth in Lin'an he learned astronomy and calendrical computation from officials of the Astronomical Bureau, and in office he held posts including county sheriff, vice prefect of Qizhou and governor of Hezhou. While mourning his mother from 1244 he wrote, at Huzhou, the Mathematical Treatise in Nine Sections (Shushu jiuzhang), prefaced in 1247: eighteen chapters with eighty-one problems in nine categories. Its 'great extension' method solves systems of simultaneous linear congruences, and its method of positive and negative root extraction sets out a full procedure for finding numerical roots of higher-degree equations. He later governed Qiongzhou and Meizhou and died in office at Meizhou around 1261, while his contemporary Zhou Mi attacked his character in the Guixin zashi notebooks.
Life and times
Dates 1208 CE–c. 1261 CE (birth by another account 1202)