Help with Math: 2.28-2.29 to 2.31-2.34

[daisy496]

Hello,
I'm lost on how to get from 2.28-2.29 to 2.31-2.34! Please help

 

[vanhees71]

Where is your specific problem?

 

[daisy496]

In the following solution, I don’t understand the math step in 7.18 to reach 7.21, can you help detail it for me please:

 

[jtbell]

There's no need to use imgur or some similar site, to post images here. Instead, use the "Attach files" button to upload image files to this forum. After they have been uploaded, you will see buttons for choosing whether to display thumbnails or the full images.

 

[vanhees71]

I also still don't know, where the specific proplem is. These are all standard manipulations with differential operators and integrals of vector calculus. There must be one specific step, where you lack understanding. Maybe we can help you, when you point at it. Otherwise we can only repeat the derivation and again most probably miss to help you with your specific problem.

 

[BvU]

There's no need to use imgur or some similar site, to post images here. Instead, use the "Attach files" button to upload image files to this forum. After they have been uploaded, you will see buttons for choosing whether to display thumbnails or the full images.

You can even just cut and paste. And if the useful part is only a fraction of the whole picture, PLEASE use snippet to copy only that part !