正四面体的四个侧面都是正三角形,是个 具有对称美的几何体．研究正四面体,对于研 究三棱锥、空间四边形,也很有帮助．可谓“麻 雀虽小,五脏俱全”．它有很多耐人寻味的性 质,下以棱长为a的正四面体为例,我们近观 正四面体． The four sides of the regular tetrahedron are regular triangles, which are symmetrical geometric bodies. Researching tetrahedrons is also helpful for studying triangular pyramids and space quadrilaterals. It can be described as “small but complete.” It has a lot of intriguing qualities. Take the regular tetrahedron with a long edge a as an example. We have a close view of the tetrahedron.