在平面几何中 ,我们常常借助一些基本图形帮助解决问题 .同样 ,我们在解决立体几何问题时 ,也需要借助一些基本图形 (如正方体、长方体等 ) .为此 ,本文介绍立体几何中一个较为特殊的四面体所具有的两个性质 ,这两个性质在求解有关空间问题时十分方便 .一、性质如图 1,P-ABO是 In plane geometry, we often use some basic graphics to help solve the problem. Similarly, when we solve the three-dimensional geometry problem, we also need to use some basic graphics (such as cubes, cuboids, etc.). For this reason, this article describes a relatively special one in three-dimensional geometry. The two properties of the tetrahedron, these two properties are very convenient when solving space problems. First, the nature of Figure 1, P-ABO is