second-order condition

例句：

1. 1. In economics, a second-order condition is a necessary condition for the existence of equilibrium.
   在经济学中，第二阶条件是达到均衡的必要条件。
2. 2. The second-order condition states that the derivative of the function must be zero at the critical point.
   第二阶条件表明函数的导数在临界点必须为零。
3. 3. The second-order condition is crucial in determining the stability of a system.
   第二阶条件在确定系统的稳定性中起着关键作用。