helical line的用法和樣例：
例句
- The existence conditions of helical equilibrium are discussed as a special configuration of the rod.
作為特殊的平衡狀態，討論桿的螺旋線平衡的存在條件。 - The stability of the helical equilibrium is analyzed with phase plane method, and an analytical criterion of stability is revealed.
用相平面法分析螺旋線平衡的穩定性，導出解析形式的穩定性條件。
