In the spherical coordinate system
$x=r \sin \theta \cos \phi$
$y=r \sin \theta \sin \phi$
$z=r \cos \theta$
$\theta$ lies in $[0,\pi]$, while $\phi$ is in $[-\pi,\pi)$. Why do we not need for the sign of $\theta$?
coordinate systemsspherical coordinates
In the spherical coordinate system
$x=r \sin \theta \cos \phi$
$y=r \sin \theta \sin \phi$
$z=r \cos \theta$
$\theta$ lies in $[0,\pi]$, while $\phi$ is in $[-\pi,\pi)$. Why do we not need for the sign of $\theta$?
Best Answer
We have
$$x=r \sin (-\theta) \cos \phi=r (-\sin \theta) \cos \phi=r \sin \theta (-\cos \phi)=r \sin \theta \cos(\phi+\pi)$$ $$y=r \sin (-\theta) \sin \phi=r (-\sin \theta) \sin \phi=r \sin \theta (-\sin \phi)=r \sin \theta \sin (\phi+\pi)$$ $$z=r \cos (-\theta)=r \cos \theta$$
So $(r,-\theta,\phi)$ represents the same point as $(r,\theta,(\phi+\pi )\pmod {2\pi})$