Ch'in Chiu-Shao

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Ch'in Chiu-Shao (秦九韶 or 秦九劭, transcribed Qin Jiushao in pinyin) (ca. 1202-1261) was a Chinese mathematician, now regarded as one of the greatest mathematicians of the 13th century. This is particularly remarkable, as Ch'in 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.

Ch'in Chiu-Shao's reputation as a mathematician lies in the Shu-shu chiu-chang (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, Ch'in included a version of the Chinese remainder theorem, which used algorithms to solve problems. In geometry, he discovered the "Ch'in Chiu-Shao'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.

Ch'in 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.