在立体几何问题的计算和证明中,经常涉及作平面的垂线问题,即怎样过P点向平面α作垂线?该问题的实质是如何过点P作平面α的垂线。面面垂直的性质定理既是解决这个问题的理论根据,同时也提供了解决这个问题的具体方法。现归纳成如下三个步骤: In the computation and verification of the three-dimensional geometry problem, the vertical line of the plane is often involved, that is, how to make a vertical line from the P point to the plane α. The essence of the problem is how to cross the vertical line of the plane α. The vertical nature theorem is not only the theoretical basis to solve this problem, but also provides a concrete method to solve this problem. It is summarized into the following three steps: