1. The problem statement, all variables and given/known data Show that, if [H,A] = 0 and dA/dt = 0, then <ΔA> is constant in time. 2. Relevant equations d<A>/dt = <i/ℏ[H,A] + dA/dt> 3. The attempt at a solution I am trying to use the above equation to show that d<ΔA>/dt is 0, and I can get to dΔA/dt = 0, but I can't figure out how to compute [H,ΔA]. The only thing I can think of is that since Δ A is just a function of A and A commutes with H, then Δ A also commutes with H, but I can't find a theorem that says that.