熟悉各种特殊三棱锥的顶点在底面上射影的位置,对于解答有关三棱锥问题是有益的,为此,我们把常见的几种特殊三棱锥的顶点在底面上的射影的位置归纳为以下几个命题,并给出简单的证明. 命题1:若三棱锥的侧棱都相等,那么顶点在底面上的射影是底面三角形的外心. Familiar with the location of the projections of the vertices of various special triangular pyramids on the bottom surface is useful for solving the problem of triangular pyramids. For this reason, we generalize the positions of the projections of the common vertices of several special trigonal pyramids on the bottom surface to the following: Propositions, and give a simple proof. Proposition 1: If the side edges of the triangular pyramid are all equal, then the projection of the vertex on the bottom surface is the outer center of the bottom triangle.