How to derive orbital angular momentum of spins in quantum mechanics?
Make up for some lost things in Griffiths QM 3rd Ed. Equation (4.134) in Griffiths QM 3rd Ed. was given but no explanation. Please explain how to derive this equation in detail or provide references that by reading them one...
A much easier way,
from
x2+y2+z2=xy+yz+zx
you can get
2x2+2y2+2z2=2xy+2yz+2zx
which equals
2x2+2y2+2z2-2xy-2yz-2zx=0
,the equivalent is
(x-y)2+(y-z)2+(z-x)2=0.