“算两次”,又称富比尼 ( G.Fubini)原理 .作为一种重要的数学解题方法 ,散见于各层级、各类型数学问题中 .其实质是将同一个量从两个不同的角度计算两次 ,利用“殊途同归”的等量关系达到“出奇制胜”的目的 .比如立体几何中求距离常用的“三棱锥体积法”(即利用三棱锥可换底 “Calculate twice”, also known as the G.Fubini principle. As an important mathematical problem solving method, it is scattered in all levels and types of mathematics problems. Its essence is to divide the same quantity from two different The angle is calculated twice, using the equal-relationship of “different paths” to achieve the goal of “surprisingly winning”. For example, the “trigonal pyramid volume method” commonly used for distance in three-dimensional geometry (that is, the use of a triangular pyramid can be used to change the bottom