Consider the initial value problem
$$
\begin{aligned}
& \dot{x}=y / z, \\
& \dot{y}=-x / z \quad(x, y, z)=(1,0,1) \text { at } t=1 . \\
& \dot{z}=1,
\end{aligned}
$$
(a) Convert this system to cylindrical coordinates $(r, \theta, \zeta)$, where $r^2=x^2+y^2$, $\zeta=z$, and $\theta=\arctan (y / x)$. Find the initial conditions in the new coordinate system.
(b) Solve the new system and show that its solution exists in the maximal interval $J=(0, \infty)$.
(c) Apply Theorem 3.10 to the new system and determine the maximal interval guaranteed by the theorem.