弦图是由四个相同的长方形拼成一个大正方形,中间还围着一个小正方形。如图1。在弦图中,大正方形ABCD 的边长等于一个长方形的长与宽之和;小正方形 A′B′C′D′的边长等于一个长方形的长与宽之差。在小学数学练习或竞赛中,有一些较复杂的题目,利用弦图知识来解答,常常会收到事半功倍的效果。请看下面的例子。例1 如图2左,街心花园中一个正方形的花坛四周有1米宽的水泥 The chord chart is made up of four identical rectangles that form a large square with a small square in the middle. Figure 1. In chord diagrams, the side length of the large square ABCD is equal to the sum of the length and width of a rectangle; the side length of the small square A'B'C'D 'is equal to the difference between the length and width of a rectangle. In elementary school math exercises or competitions, there are some more complicated topics that are solved by knowledge of chord diagrams and often receive a multiplier effect. Please see the example below. Example 1 As shown in Figure 2 left, there is a 1 meter wide cement around a square flower bed in the heart of the garden