The sign of decentralization in the field of higher numbers

1.

Details are shown in the figure

if you have any doubts, please ask

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2.

Integral mean value theorem

3. Download the "mathematical formula editor" from the Internet. Now there is version 6.7 in Chinese culture
there are almost all the symbols commonly used in mathematics here. And it's easier to master
the installation method can be completed step by step according to the prompts
if you don't know, ask again.

4. The equivalent infinitesimal substitution is the same as SiNx ~ X.

5. It's the integral in the region a, and then Da is the differential. Here a should be the area on the surface