在物理课上，老师解释了如何使用拉格朗日函数来描述弹簧系统的运动。

In physics class, the teacher explained how to use the ___Lagrangian to describe the motion of a spring system.

航天器被放置在拉格朗日点，以保持稳定的轨道位置。

The spacecraft was placed at a ___Lagrangian point to maintain a stable orbital position.