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## Homework Statement

Basically need to use einstein's summation convention to find the grad of (mod r)^n and a.r where a is a vector and r = (x,y,z)

## Homework Equations

## The Attempt at a Solution

Not sure where to begin really.. :S

grad (mod r)^n= (d/dx, d/dy, d/dz) of root (X

_{1}^2 + x

_{2}^2 + x

_{3}^2)^n..

Just not sure what to do now..

thanks