The divergence of F:
Implement the integral of over the interior of :
=
To compute the flux through , note that there are two boundaries, the upper elliptic paraboloid, and the ellipse and its interior that is the intersection of the paraboloid and the plane . To compute the flux through the upper surface, note that on that surface
|
|
|
|
|
|
|
|
If this be integrated over the ellipse , the result is
=
On the lower boundary (ellipse), the outward normal is , so , which becomes zero in the plane . Hence, the flux through the interior of the ellipse at the bottom of vanishes, and the flux through the upper surface matches the volume integral of the divergence.