平面几何中有一类解比例线段的问题，通常作法是作辅助线（如平行线）或利用三角形相似或利用与之相关的定理（如梅涅劳斯定理）来解决．这些方法对学生的识图能力、逻辑思维能力等有着较高的要求．本文试图利用一个公式，从代数的角度，用“计算”的方法简洁地解决这类问题． There is a problem of solving proportional line segments in plane geometry. Usually, this is done as an auxiliary line (such as a parallel line) or using a triangle similarity or a related theorem (such as the Menelaus theorem) to solve. These methods have higher requirements for the students’ ability to read maps and logical thinking. This paper attempts to use a formula to solve this type of problem from the algebraic point of view using the “calculation” method.