I'm taking advantage of the fact that start is going to be a point, and I'm just directly saying, John give me your x-value.

我利用了开始是一个点这个事实,然后我就直接说，返回给我你的x值，因此我不知道。

麻省理工公开课 - 计算机科学及编程导论课程节选

And that's the following. Let's take a particle that is moving in the x-y plane, so that at one instance-- sorry, let me change this graph-- is here--oh, this is bad.

接下来,我们来看一个物体,在 x-y 平面内运动,在这个例子中,对不起,我要重画一下这个图,在这里,这画得不好

耶鲁公开课 - 基础物理课程节选