hi :) it's me again. This is my second question in a few days, w/o being able to help anyone else, hope to be not too much pretentious(adsbygoogle = window.adsbygoogle || []).push({});

my doubt this time regards the mathematical passage underneath the formula (23) of this speech:

http://scarface.ngi.it/elet.jpg [Broken]

disregard the text part because i don't think it's helpful in an english forum it just introduces the electric field and its properties.

The fact is I cannot understand the derivation done from the E formula, i thought that the thing to do was just derivating r (that, considering an orthogonal system with the origin in the (x0,y0,z0) point, is (x^2+y^2+z^2)^1/2) because i had to consider the rest as costant so out of the derivation but it isn't it.. any help? thanks

alex

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# Electric field, mathematical problem

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