I could take an unknown gas and put it in and measure it and then say, wow, those are the lines that are characteristic of sodium.

我取一种未知气体，把它放到管里,然后检测它，哇，这些线是钠的特征。

麻省理工公开课 - 固态化学导论课程节选

Therefore, it'll compress by an unknown x, which is equal to mg divided by the force constant of the spring.

因此它的压缩量为 x,也就等于 mg 除以弹簧的弹性系数

耶鲁公开课 - 基础物理课程节选

The mathematical theory of probability was unknown until that time and you can see that insurance suddenly made an appearance at that time.

在那之前,概率的数学理论,是不存在的,而随着概率论的出现,保险业也突然出现了

耶鲁公开课 - 金融市场课程节选

So, what we have found out so far, I'm purposely going from x to y because I want you to know that the unknown variable can be called an x or can be called a y.

到目前为止,我们有这些结论,我特地把x换成y,因为我想让你们明白,未知变量既可以写成x,也可以写成y

耶鲁公开课 - 基础物理课程节选