那部分是数学的东西，即散度定理。

At that part is actually math, namely, the divergence theorem.

youdao

在某种方式下它们是有联系的,这就是散度定理。

OK, so we have somehow a connection between these which is the divergence theorem.

youdao

第二点信息是，我们从散度定理得到的，这就是我花费时间试图解释的。

And the second piece of information that we got was from the divergence theorem, and that was the one I spent time trying to explain.

youdao