我们知道直角三角形在三角形当中是一类特殊的三角形,具有很大的研究价值,得到了很多有用的结论。那么在推广到三维空间,在所有的四面体中也有一类比较特殊的四面体叫做直四面体,经常在各类高考模拟考试中出现,本文对其进行探讨,得到一些重要的结论.直四面体的定义:如图1所示,在四面体P-ABC中,侧棱PA, We know that right-angled triangle in the triangle is a special kind of triangle, with great research value, has been a lot of useful conclusions. So in the promotion to three-dimensional space, in all tetrahedron also has a rather special tetrahedron called tetrahedron, often appear in various types of college entrance examination simulation examinations, this article discusses, get some important conclusions. Straight four sides Body definition: As shown in Figure 1, in the tetrahedral P-ABC, the side edges PA,