中国古代的代数是与几何分不开的。例如,几何中的出入相补原理就在方程理论中有广泛的应用.早在西汉末年成书的《九章算术》中,就已经用出入相补原理解简单的二次方程了.方程理论发展到宋元,已趋于成熟,出入相补原理仍然是列方程的一个有力工具。本文将着重讨论这一原理在十三世纪《益古演段》中的应用. Ancient Chinese algebra is inseparable from geometry. For example, the principle of complementarity in geometry is widely used in the theory of equations. As early as the “Nine Chapters of Arithmetic” written in the end of the Western Han Dynasty, a simple quadratic equation has been used to understand the simpler equations. By the Song and Yuan dynasties, maturity has matured, and the principle of in- and out-complementation is still a powerful tool for formulating equations. This article will focus on the application of this principle in the 13th century “Yigu drama”.