So what they do is, they're describing how these thermodynamic properties change, in terms of only state functions and state variables.

他们的作用是描述,随着状态函数和状态变量的变化，系统的热力性质如何变化。

麻省理工公开课 - 热力学与动力学课程节选

Since we're talking about wave functions, since we're talking about the properties of waves, we don't only have constructive interference, we can also imagine a case where we would have destructive interference.

因为我们讨论的是波函数，因为我们讨论的是波的性质，我们不仅有相长干涉，我们也可以想象在,某种情况下会有相消干涉。

麻省理工公开课 - 化学原理课程节选

You can square this guy and add it to the square of this guy and you will find, using the magic of trigonometry, that this is true.

你可以把这两个式子平方相加,再用一下三角函数的性质,你会发现这是正确的

耶鲁公开课 - 基础物理课程节选