平面图形折叠的空间问题,关键是寻求折叠前后的不变量,利用平面图形和空间图形之间的关系进行计算,用空间概念解决问题.如何寻求折叠问题中的不变量呢?把握折叠前后的部分图形是否在同一个平面上,若在同一个平面上,则折叠前后的长度、角等就是不变量.把握折叠问题中的不变量就 The key to the space problem of folding a plane figure is to find invariants before and after folding, use the relationship between plane graphics and spatial graphics to calculate, use spatial concepts to solve problems, how to seek invariants in folding problems, and grasp the parts before and after folding Whether the figures are on the same plane, if they are on the same plane, the lengths and angles before and after folding are invariants. Grasping the invariants in the folding problem