“三垂线定理”是立体几何中的一个重要定理,它不但联系着一系列主要概念(如平面的垂线、斜线、斜线在平面内的射影等),而且其证明中又包含有较为典型的证题方法(线面垂直与线线垂直证法),并且有着广泛的应用。因而这一定理是立几数学中的重点。又因其牵涉到的概念较多,故又是教学中的难点。下面就笔者在教学中的作法谈一点体会,以就教于同行诸君。一、引导学生发现矛盾,造成悬念,激发学 The “Triple vertical line theorem” is an important theorem in the three-dimensional geometry. It not only links a series of major concepts (such as a plane perpendicular line, slashes, oblique projections in the plane, etc.), but its proof contains The more typical method of proofs (vertical vertical line and line vertical proof method), and has a wide range of applications. Therefore, this theorem is the focus of several mathematics. Because of the many concepts involved, it is also a difficulty in teaching. The following discussion of the author’s teaching in the practice, in order to teach their peers. First, guide students to discover contradictions, cause suspense, stimulate learning