“四脚钉”是美国警察用来堵截肇事车辆的一种路面布撒物,其结构能使它任意抛制在水平地面上后总有一脚竖直向上,从而扎破肇事车轮胎,迫使肇事车辆停车,试问如何构造四脚钉?图1如图1,由于四脚钉任意水平放置,一脚总要竖直向上,故四脚应等长,设为a,四角两头成等角,θ向上一脚OD The “four-legged nail” is a pavement spread used by American police to intercept traffic accidents. Its structure enables it to arbitrarily cast on a horizontal floor and has a foot upright, which breaks the tire of the vehicle and forces the accident. Vehicle parking, how to construct a four-legged nail? Figure 1 As shown in Figure 1, because the four-legged nails are placed horizontally, one foot should always be upright. Therefore, the four feet should be equal in length, set to a, and the four corners should be equal angles, θ Up one foot OD