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Homework Help: Divergence theorem/vector calculus

  1. Mar 10, 2010 #1
    1. The problem statement, all variables and given/known data

    I want to show that:

    Grad dot product with r = 2/r

    r is the unit vector r/r
    r = xi + yj + zk
    r is magnitude of r

    3. The attempt at a solution

    I think the answer should be 3/r

    since unit vector r = r/r,
    r = (x/r)i + (y/r)j + (z/r)k

    then when I do grad dot r I should get (1/r) + (1/r) + (1/r) = (3/r)

    what do you think?
  2. jcsd
  3. Mar 10, 2010 #2


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    Science Advisor
    Homework Helper

    I think you are ignoring the fact that r=sqrt(x^2+y^2+z^2) and so r depends on x, y and z.
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