If the question of time is not explicitly brought up, then you should know that you have to use this formula.

如果时间的问题并没有明确提出,那你应该知道,必须要用这个式子

耶鲁公开课 - 基础物理课程节选

So this you should be able to know pretty quickly, so let's just take 10 seconds here.

大家应该很快就能看出来，所以让我们只花十秒钟的时间来做一下。

麻省理工公开课 - 化学原理课程节选

So you should know when you look at a graph like this what it's doing.

因此当你看到这样一个图表时,要知道它是怎样运动的

耶鲁公开课 - 基础物理课程节选

Now many of you may have heard, many of you may know, and if you don't already know this, I should warn you, that I have a reputation around Yale as being a harsh grader.

你们中的大多数可能听说过，你们中的一部分可能知道，如果你真的不知道，那么我要警告你，我在耶鲁,是出了名的严厉。

耶鲁公开课 - 死亡课程节选

Again, you should make sure you know how to derive this.

你们还是要知道这是怎么得来的

耶鲁公开课 - 基础物理课程节选

This vector i prime has got a horizontal part, This kind of trigonometry you should know all the time.

矢量 i' 有一个水平方向的分量,这类三角关系你们应该已经很熟悉了

耶鲁公开课 - 基础物理课程节选