Divergence theorem/vector calculus

[t_n_p]

Homework Statement

I want to show that:

Grad dot product with r = 2/r

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

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?

 

[Dick]

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.