arc boutant

例句：

1. 1. The arc of the circle is a perfect circle.
   圆的弧是一个完美的圆。
2. 2. The parabola passes through the center of the sphere.
   抛物线经过球体的中心。
3. 3. The arc length is equal to the distance from the center to the endpoint of the arc.
   弧长等于从中心到弧端点的距离。