摆线是数学中众多的迷人曲线之一．它是这样定义的：一个圆沿一直线缓慢地滚动，则圆上一固定点所经过的轨迹称为摆线-Cycloid is a curve in mathematics, one of the many charming. It is defined as: a circle rolling along a straight line slowly, then the circle of a fixed point through which the track is called cy