# Homework Help: Commutators for functions of operators (momentum/position)

1. May 16, 2012

### Ratpigeon

1. The problem statement, all variables and given/known data

show that [x,f(p_x)] = i $\hbar$ d/d(p_x) f(p_x)

2. Relevant equations

x is the position operator in the x direction, p_x is the momentum operator; i $\hbar$
d/dx
[x, p_x]=xp-px
3. The attempt at a solution
I'm stuck. maybe chain rule for d/dx and d/d(p_x)...? But I don't see how I'd do it...

2. May 17, 2012

### Ratpigeon

Never mind - I had to reqresent it as a power series, and then it was easier