1, Introduction: Chord diagram, invented by Zhao Shuang in the Three Kingdoms period, is the most important geometric method to prove Pythagorean theorem. In 2002, the International Congress of Mathematicians was held in Beijing. The emblem of the congress is a "string diagram" drawn by Zhao Shuang, an ancient mathematician in China, which embodies the inheritance and development in mathematical research.
2. Brief introduction of the inventor: Zhao Shuang, whose native place and year of birth and death are unknown. Also known as Baby, the word Jun Qing. China ancient mathematician and astronomer. During the Three Kingdoms period, people from Wu, namely Wei Jin people or Han people, lived in the early 3rd century. He studied Zhang Heng's astronomical mathematics works and Liu Hong's dry calendar, and also mentioned nine chapters of arithmetic. His main contribution is that he deeply studied Zhou Kuai Shu Jing for about 222 years, prefaced it and made detailed comments.
3. Origin: Zhao Shuang claimed to have idle days with negative salary, studied Zhou Xie, and made notes on it, which shows that he is a mathematician who is not divorced from manual labor. It is generally believed that The Book of Zhou Bi suan Jing was written around 100 BC, and it is an astronomical work that uses mathematical methods such as fractional operation and Pythagorean theorem to explain the theory of Gaitian. The Nine Chapters Arithmetic, written almost at the same time, clearly put forward the Pythagorean theorem and some problems in solving Pythagorean forms. Zhao Shuang's Jing Zhu of Zhou Chuanshu explains the scripture of Zhou Chuanshu paragraph by paragraph.