tian yuan

The "method of the celestial unknown," or tian yuan, was an algebraic computation method developed in China, primarily using counting rods. This technique, detailed in works like Li Ye's "Sea Mirror of Circle Measurements" and Zhu Shijie's "Precious Mirror of the Four Elements," allowed mathematicians to solve problems by setting up and manipulating polynomial equations. It was particularly useful for calculating dimensions of geometric figures. While a significant achievement, this method was largely forgotten by the 16th century, only to be rediscovered and understood again with the help of Western algebra in the 18th century.123