如图1,从长方体中砍下一个角,可以得到直角四面体PABC.反之,对于直角四面体,我们可以将它补成长方体用以解题,这是立体几何中已经司空见惯的一种补形解法.本文介绍对于一般四面体都适用的另一种补形解法.如图2,从平行六面体中砍下四个角,可以得到四面体ABCD.反之,我们可以将四 In Figure 1, cutting a corner from a rectangular parallelepiped can give a right-angled tetrahedron PABC. Conversely, for a right-angled tetrahedron, we can add it to a cuboid to solve the problem. This is a kind of complement that has become commonplace in solid geometry. Solution. This article describes another complement solution that is applicable to the general tetrahedron. As shown in Figure 2, cutting off the four corners from the parallelepiped can give the tetrahedron ABCD. Conversely, we can use four.