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

We could do it dy dx. Or, maybe we will want to actually make a change of variables to first shift this to the origin, x-2 you know, change x to x minus two and then switch to polar coordinates.

也可以dy，dx来划分，或者,对变量做一下变化，移动到原点，就是把x变成,然后再转化成极坐标。

youdao

If you end up with a dx, dy, dz in the surface integral, something is seriously wrong.

如果在这个曲面积分中是以dx, dy, dz结尾的，则表明出现了很大的问题。

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

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