The expression is the third component of = , where a third-component of zero has been appended to so that its curl could be calculated.
The integral of this expression over can be obtained if the ellipse is given in polar coordinates by . The left-hand side of the Stokes-form of Green's theorem is therefore
=
The right-hand side of the Stokes-form of Green's theorem is the line integral of the tangential component of around the ellipse . Parametrize the ellipse as , so that the line integral becomes
=
Note that this second parametrization of the ellipse does not use polar coordinates.