1. The problem statement, all variables and given/known data let A be a lowering operator. 2. Relevant equations Show that A is a derivative respects to raising operator, A†, A=d/dA† 3. The attempt at a solution I start by defining a function in term of A†, which is f(A†) and solve it using [A , f(A†)] but i get stuck after that. Can someone please explain briefly what i should do in the next step?