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Homework Statement
Show [itex] \frac{d}{dt}\langle\bf{L}\rangle = \langle \bf{N} \rangle[/itex] where [itex]\bf{N} = \bf{r}\times(-\nabla V)[/itex]
2. Homework Equations .
[tex]\frac{d}{dt}\langle A \rangle = \frac{i}{\hbar} \langle [H, A] \rangle [/tex]
The Attempt at a Solution
I get to this point: [itex]\frac{i}{\hbar}\langle [H,L] \rangle = \frac{i}{\hbar}\langle [H, r \times p] \rangle [/itex] and then I'm stuck. I know the next step is supposed to use something like [itex][H, r \times p] = [H,r] \times p + r \times [H,p][/itex] but I don't see how to get this. I don't understand how operators distribute over the cross-product. Can anyone help or point me to some online resource where I can study how to work with operators/commutators/ etc.? I've been searching the internet all day with little to show for it.