And if it is going to be a standing wave then this must be an integral number of wavelengths.

如果这有个驻波的话,那么周长就是个整数。

麻省理工公开课 - 固态化学导论课程节选

Even if the thing that you really want is an integral that would be difficult to evaluate.

即使需要计算的,是一个很难的积分。

麻省理工公开课 - 热力学与动力学课程节选