Index Notation: ∂_i 1/r = -x_i/r^3?

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SUMMARY

The discussion centers on the index notation expression ∂_i 1/r = -x_i/r^3, which confuses participants. The expected result of -x_i/r^2 is clarified through the application of the chain rule, specifically ∂r/∂x and ∂r/∂i = x_i/r. This highlights the importance of understanding the relationship between variables in index notation and the derivatives involved.

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  • Familiarity with the chain rule in calculus
  • Basic knowledge of partial derivatives
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Students and professionals in mathematics, physics, and engineering who are dealing with index notation and derivatives in their work.

ellocomateo
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Hello world,

Index notation is driving me crazy: why on Earth is ∂_i 1/r = -x_i/r^3 ?

I would expect it to be -x_i/r^2...

Thanks for commenting
 
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welcome to pf!

hello ellocomateo! welcome to the world! :smile:

(try using the X2 and X2 buttons just above the Reply box :wink:)

∂r/∂x = … ? :wink:
 
Oh, you mean chain rule and ∂r/∂i=xi/r
Thanks!
 

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