如果定义了用户退出将在这里调用。

If a user exit is defined, it will be invoked at this juncture.

youdao

如果定义了用户退出将激活它。

If a user exit is defined, that exit will be invoked.

youdao

如果定义了此方法，则在该上下文中调用对象时将使用此方法。

If this method is defined, it will be used when the object is called in that context.

youdao

If you plug in x equals one that is our series.

如果你定义x等于1这就得到了我们的式子。

麻省理工公开课 - 固态化学导论课程节选