Li Rui

Li Rui

(born Jan. 15, 1769, Yuanhe, China—died Aug. 12, 1817, Yuanhe) Chinese mathematician and astronomer who made notable contributions to the revival of traditional Chinese mathematics and astronomy and to the development of the theory of equations. Having failed the Chinese civil service examinations several times, he could obtain no official position and had to make a poor living as an assistant to various mandarins. From about 1800 he began to study the works of the 13th-century mathematicians Li Ye and Qin Jiushao. He found that traditional Chinese methods of solving higher-degree equations had several advantages over algebraic methods that had been recently imported from the West. His Kaifang shuo (1820; “On the Method of Extraction”) contains his work on the theory of equations: a rule of signs, a discussion of multiple roots and negative roots, and the rule that nonreal roots of an algebraic equation must exist in pairs.