Solution
= Solution
The conversion from <cylindrical coordinates> to <Cartesian coordinates> is
$$
\boxed{x=\rho\cos\phi,\qquad y=\rho\sin\phi,\qquad z=z.}
$$
Here $\rho\geq0$ is the distance from the $z$ axis and $\phi$ is measured around that axis. A full turn $\phi\mapsto\phi+2\pi$ describes the same point.