立体几何中的有些问题表面上看来难以解决,但只要我们能够创造性地运用已知图形中的某些信息,并以其为原料、所求结论为目标,合理地运用数学知识、数学方法和数学思想,就可以构建出符合条件的已经解决或比较容易解决的几何模型.运用这些几何模型解题,能够收到形象直观、简捷明快、出奇制胜、耐人寻味的效果,而且能够优化思维,探求 Some problems in the three-dimensional geometry seem difficult to solve on the surface, but as long as we can creatively use some of the information in known graphics, and use it as a raw material, the goal of the conclusions, the rational use of mathematical knowledge, mathematical methods and Mathematical thinking can be constructed to meet the conditions of the geometric model has been resolved or relatively easy to solve. The use of these geometric models to solve problems, can receive the image intuitive, simple and bright, surprisingly successful, thought-provoking effect, but also to optimize the thinking, search