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'Qin Jiushao' (, ca. 1202–1261), courtesy name 'Daogu' (道古), was a Chinese mathematician born in Ziyang, Sichuan, his ancestry was from Shandong, and is now regarded as one of the greatest mathematicians of the 13th century. This is particularly remarkable, as Qin did not devote his life to mathematics. He was accomplished in many other fields, however, and held a series of bureaucratic positions in several Chinese provinces.
Qin’s reputation as a mathematician lies in the ''Shùshū Jiǔzhāng'' (“Mathematical Treatise in Nine Sections”), issued in 1247. The treatise covered matters that ranged from indeterminate analysis to military matters and surveying. In the treatise, Qin included a version of the Chinese remainder theorem, which used algorithms to solve problems. In geometry, he discovered “Qin Jiushao's formula” in finding the area of a triangle with given length of three sides. This is the same as Heron’s formula, discovered earlier.
Qin recorded the earliest explanation of how Chinese calendar experts calculated astronomical data according to the timing of the winter solstice. Among his accomplishments are introducing techniques for solving equations, finding sums of arithmetic series, and solving linear systems. He also introduced the use of the zero symbol in Chinese mathematics.

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References

★ Guo, Shuchun, "Qin Jiushao". ''Encyclopedia of China'' (Mathematics Edition), 1st ed.

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★ Simon Fraser University biography for “Qin Jiushao”