Homework Help: Commutation proof

1. Apr 18, 2006

precondition

Hi there, I need a help on one of the commutation proof,
the question is, show that [Lx,L^2]=0 cyclic where L=l1+l2
The expression simplifies to [Lx,l1l2]+[Lx,l2l1] but I'm not sure if they are 0.

2. Apr 18, 2006

dextercioby

What does L=l1+l2 mean ...?

Daniel.

3. Apr 18, 2006

Meir Achuz

write L_x=L1_x+L2_x
and expand L^2=(L1+L2)^2=...