Let's say you have to go through three or four operations to get a final number, well, do it algebraically.

让我们说,你不得不通过3-4个操作,才能得到最终的数，好吧，用代数方法求解。

麻省理工公开课 - 固态化学导论课程节选

So we have four choices in terms of initial and final energy levels, and also what it means - in terms of the electron -- whether it's gaining energy or whether it's going to be emitting energy?

我们有这四个选项,各有不同的初始能量和末能量,它都是按照电子来说的,不管是失去能量还是得到能量？

麻省理工公开课 - 化学原理课程节选