Ok, I know $div \vec r=3$.
$\vec r = r_x\vec i+r_y\vec j + r_z\vec k$.
$(\frac{\partial}{\partial x}i+\frac{\partial}{\partial y}j+\frac{\partial}{\partial z}k, r_xi+r_yj+r_zk)=\frac{\partial r_x}{\partial x} + \frac{\partial r_y}{\partial y} + \frac{\partial r_z}{\partial z}$
Now this supposedly gives $1+1+1$. How do I start seeing that?
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$\begingroup$Note that the radial vector has its component as $$ \vec{r} =\langle x,y,z \rangle $$ Thus the divergence is $$ \operatorname{div} \vec{r} = \frac {\partial x}{\partial x} +\frac {\partial y}{\partial y}+\frac {\partial z}{\partial z} =1+1+1 =3$$
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