envelope of curves

例句：

1. 1. The envelop of curves is the region where the surface of a curved object touches the plane of a flat surface.
   曲线的包络是曲线物体的表面与平面接触的区域。
2. 2. The envelop of curves is used to describe the shape of an object when it is viewed from above or below.
   曲线的包络用于描述物体从上方或下方观察时的形状。
3. 3. The envelop of curves can be used to calculate the volume and surface area of a solid object.
   曲线的包络可以用来计算固体物体的体积和表面积。