• Journal for History of Mathematics
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• v.29 no.1
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• pp.1-16
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• 2016

This study analyzes the contents and expression methods of Jeong Yag-yong's "Gugo Wonlyu". The 530-page long "Gugo Wonlyu" discusses 1541 formulas about Gu, Go, Hyun, Hwa, Gyo; however, it has only the results of formulas and no explanations about their inducement method. Therefore we do not know how he derives and verifies the formulas. In addition, it did not follow the basic form of oriental mathematics textbooks: problem-answer-solution, and presented all the formulas only with characters without using numbers. This is a very distinctive aspect compared to other mathematical textbooks. In addition, the formulas about 5-Hwa and 5-Gyo are addressed exactly in fixed order and covers a formula in various directions. This is a clear evidence that Jeong Yag-yong analyzed and studied the Gugosul thoroughly.

• Journal for History of Mathematics
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• v.32 no.3
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• pp.97-108
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• 2019

This paper is an outgrowth of a study on recent papers and presentations of Hong Sung Sa, Hong Young Hee and/or Lee Seung On on Gugo Wonlyu which is believed to be written by the famous Joseon scholar Jeong Yag-yong. Most of what is discussed here is already explained in these papers and presentations but due to brevity of the papers it is not understood by most of us. Here we present them in more explicit and mathematical ways which, we hope, will make them more accessible to those who have little background in history of classical Joseon mathematics. We also explain them using elementary projective geometry which allow us to visualize Pythagorean polynomials geometrically.

• Journal for History of Mathematics
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• v.29 no.5
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• pp.257-266
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• 2016

This paper is a sequel to our paper [3]. Although polynomials in the tianyuanshu induce perfectly the algebraic structure of polynomials, the tianyuan(天元) is always chosen by a specific unknown in a given problem, it can't carry out the role of the indeterminate in ordinary polynomials. Further, taking the indeterminate as a variable, one can study mathematical structures of polynomials via those of polynomial functions. Thus the theory of polynomials in East Asian mathematics could not be completely materialized. In the previous paper [3], we show that Jeong Yag-yong disclosed in his Gugo Wonlyu(勾股源流) the mathematical structures of Pythagorean polynomials, namely polynomials p(a, b, c) where a, b, c are the three sides gou(勾), gu(股), xian(弦) of a right triangle, respectively. In this paper, we show that Jeong obtained his results through his recognizing Pythagorean polynomials as polynomial functions of three variables a, b, c.

• Journal for History of Mathematics
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• v.28 no.6
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• pp.301-310
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• 2015

Since Jiuzhang Suanshu, the main tools in the theory of right triangles, known as Gougushu in East Asia were algebraic identities about three sides of a right triangle derived from the Pythagorean theorem. Using tianyuanshu up to siyuanshu, Song-Yuan mathematicians could skip over those identities in the theory. Chinese Mathematics in the 17-18th centuries were mainly concerned with the identities along with the western geometrical proofs. Jeong Yag-yong (1762-1836), a well known Joseon scholar and writer of the school of Silhak, noticed that those identities can be derived through algebra and then wrote Gugo Wonlyu (勾股源流) in the early 19th century. We show that Jeong reveals the algebraic structure of polynomials with the three indeterminates in the book along with their order structure. Although the title refers to right triangles, it is the first pure algebra book in Joseon mathematics, if not in East Asia.