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Homework Statement
A is a Hermitian operator which commutes with the Hamiltonian: \left[A,H\right]=AH-HA=0
To be shown: \frac{d}{dt}A=0
Homework Equations
Schrödinger equation: i\hbar\frac{\partial}{\partial t}\psi=H\psi with the Hamilton operator H.
The Attempt at a Solution
I have seen this solution on many sites:
\frac{d}{dt}<A>=\frac{d}{dt}<\psi|A|\psi>=<\psi|\frac{\partial A}{\partial t}|\psi>+<\frac{d\psi}{dt}|A|\psi>+<\psi|A|\frac{d\psi}{dt}>=<\frac{\partial A}{\partial t}>+\frac{1}{i\hbar}<\left[ A, H\right] >=0
I have a problem with this: <\frac{d\psi}{dt}|A|\psi>+<\psi|A|\frac{d\psi}{dt}>=\frac{1}{i\hbar}<\left[ A, H\right] >
Okay, obviously we have from the Schrödinger equation:
H=i\hbar\frac{\partial}{\partial t}
and thus
\frac{\partial}{\partial t}=\frac{1}{i\hbar}H
and thus
<\frac{d\psi}{dt}|A|\psi>+<\psi|A|\frac{d\psi}{dt}>=\frac{1}{i\hbar}(<H\psi|A|\psi>+<\psi|A|H\psi>)=\frac{1}{i\hbar}<\psi|HA+AH|\psi>
But this is not the commutator but the anti-commutator. It is plus and not minus! What did I do wrong here?