Index Notation: ∂_i 1/r = -x_i/r^3?

[ellocomateo]

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

 

[tiny-tim]

welcome to pf!

hello ellocomateo! welcome to the world!

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

∂r/∂x = … ?

 

[ellocomateo]

Oh, you mean chain rule and ∂r/∂_i=x_i/r
Thanks!