@TedShifrin I found it at the following exercise I am looking at:
We are given the following point in cylindrical coordinates. Write it in orthogonal and spherical coordinates.
The point is $\left (2, \frac{\pi}{2}, -4\right )$.
I have done the following:
The cylindrical coordinates are of the form $(r, \theta , z)$, that are defined by $x=r \cos \theta , y=r \sin \theta , z=z$.
The orthogonal coordinates are of the form $(x, y, z)$.
$x=r \cos \theta=2 \cos \frac{\pi}{2}=0 , y=r \sin \theta =2 \sin \frac{\pi}{2}=2 , z=z=-4$