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## Homework Statement

if [tex]\phi[/tex] =

**r**

**k**/r[tex]^{3}[/tex] where

**r**=x

**i**+ y

**J**+ z

**k**and r is the magnitude of

**r**, prove that [tex]\nabla[/tex][tex]\phi[/tex] = (1/r[tex]^{}5[/tex])(r[tex]^{}2[/tex]

**k**-3(

**r**.

**k**)

**r**

so i differenciated wrt x then y then z and tried to tidy it all up but i got1/rClick to see the LaTeX code for this image(-3(r.k)r)

When i differenciated wrt x i got -3x/rClick to see the LaTeX code for this image and similar for y and z was this right?

then i just put these answers into Click to see the LaTeX code for this image = dx/dClick to see the LaTeX code for this image i + dy/dClick to see the LaTeX code for this image j + dz/dClick to see the LaTeX code for this image k

which gives

-3xz/rClick to see the LaTeX code for this image i - 3yz/rClick to see the LaTeX code for this image j - 3zz/rClick to see the LaTeX code for this image k

am i right so far? it just seemed to tidy up to 1/rClick to see the LaTeX code for this image(-3(r.k)r)

when it should be 1/rClick to see the LaTeX code for this image(rClick to see the LaTeX code for this imagek-3(r.k)r)