So, instead of setting up the integral with bounds and integrating dx dy or dy dx or in polar coordinates, I'm just going to say, well, let's remember the definition of a center of mass.

那么我们将不会建立带上下限的积分，和积分dx, dy, dy, dx或者在极坐标做线积分，需要说，让我们回忆一下质心的定义。

youdao

youdao

youdao

You all know that when you do dy/dx, you're not supposed to cancel that d.

你们都知道 当你算dy/dx时,你不能把d约掉

耶鲁公开课 - 基础物理课程节选