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## Homework Statement

**v**= (

**a**.

**r**)

**r**where

**r**=x

**i**+y

**j**+z

**k**and

**a**is a constant vector

show [tex]\nabla[/tex].

**v**= 4(

**a**.

**r**)

I let

**a**= a

**i**+b

**J**+c

**k**

then (

**a**.

**r**) = ax+by+cz

then this (

**a**.

**r**)

**r**= ax[tex]^{2}[/tex]

**i**+by[tex]^{2}[/tex]

**j**+cz[tex]^{2}[/tex]

**k**

[tex]\nabla[/tex].

**v**= da1/dx+da2/dz+da3/dz =2ax+2by+2cz

which is equal to 2(

**a**.

**r**)

am i wrong or the book?