Solution
= Solution
In the <cylindrical coordinate system>, $r=\sqrt{x^2+y^2}=5$ and $z=-1$. The point is in the third quadrant, so a representative azimuth in $[0,2\pi)$ is $\pi+\arctan(4/3)$. Therefore
$$
\boxed{(r,\theta,z)=\left(5,\ \pi+\arctan\frac43,\ -1\right)}.
$$
The angle is defined modulo $2\pi$.