由于平面图形远比立体图形简单、清晰,因此,把立体图形设法展开在平面上,是简化和解决某些立体几何问题的重要途径。可是,通常见到的应用之例,却局限在一类极小问题上。如求长方体、棱柱、棱锥以及圆柱、圆锥等可展曲面上之两点间的最短路线。其实,这种展开的方法亦可用来解决其他一些立体几何的问题。试看下例。 Because the planar graphic is much simpler and clearer than the three-dimensional figure, trying to expand the three-dimensional figure on the plane is an important way to simplify and solve some problems of three-dimensional geometry. However, the commonly seen examples of applications are limited to one type of minimal problem. For example, the shortest line between two points on a developable surface such as a rectangular solid, a prism, a pyramid, and a cylinder, a cone, and the like. In fact, this method of deployment can also be used to solve other problems of solid geometry. Take a look at the following example.