# Commutative in Quantum Mechanics

1. Apr 11, 2014

1. The problem statement, all variables and given/known data
Calculate the commutative
[P2,Lx]
2. Relevant equations
P2=P2x+P2y+P2z
[Py,Lx]=-iħPz
[Pz,Lx]=iħPy
[Px,Lx]=[Py,Ly]=[Pz,Lz]=0
3. The attempt at a solution
[P2,Lx]=[P2x+P2y+P2z,Lx]
=[P2x,Lx]+[P2y,Lx]+[P2z,Lx]
=Px[Px,Lx]+[Px,Lx]Px+Py[Py,Lx]+[Py,Lx]Py+Pz[Pz,Lx]+[Pz,Lx]Pz
=-iħ[Py+Py]+iħ[Pz+Pz]
=iħ[P2z+P2y]

Last edited: Apr 11, 2014
2. Apr 11, 2014

### tman12321

First off, what is your question? Second off, your commutation relations are wrong. For example, [P2,L1]=-iħP3.

3. Apr 11, 2014

Thanks, I was edited the given (miss-writing)
The question is written in the first step
Calculate the commutative [P^2,Lx]=?

4. Apr 11, 2014

### tman12321

Yes, but what is the question you have about how to do this? You've fixed the typo, but you haven't applied the changes to your solution.

Last edited: Apr 11, 2014
5. Apr 11, 2014

6. Apr 11, 2014

### tman12321

As I said before, you've fixed the typos in your "Relevant Equations", but you haven't applied these changes to your solution.

7. Apr 12, 2014