Solution (source code)

= Solution

In <spherical coordinates>, $z=r\cos\theta$ and $x^2+y^2=r^2\sin^2\theta$, so the <elliptic paraboloid> has equation
$$
\boxed{r\cos\theta=r^2\sin^2\theta.}
$$
Away from the origin this is $r=\cos\theta/\sin^2\theta$, with $0<\theta<\pi/2$. The undivided equation also includes the origin, where angular coordinates are not unique.