众所周知,圆是我们现实生活中应用比较广泛的几何图形之一,也是历年各地中考的热点内容,为了方便同学们的学习,现以中考试题为例说明如下.例1 (烟台市)如图1,用一块直径为a的圆桌布平铺在对角线长为a的正方形桌面上,若四周下垂的最大长度相等,则桌布下垂的最大长度x为( ) As we all know, the circle is one of the more widely used geometric figures in our real life, and it is also a hot topic in various examinations over the years. In order to facilitate the students’ learning, we take the middle exam questions as an example to illustrate the following. Example 1 (Yantai City) Figure 1 , with a diameter of a circular tablecloth tiled on a square table with a diagonal length a, if the maximum length of the surrounding sagging is equal, then the maximum length x of the tablecloth sagging is ()