1. The problem statement, all variables and given/known data: I would like to know if the definition of the ZSR response means that the initial condition at any t0 needs to be 0. 2. Relevant equations: lets say : we're trying to calculate the ZSR response from a first order equation of the voltage of a capacitor and the initial condition is: Vc(t0)=V0, Vc'(t)+(1/RC)*Vc(t)=X(t)/C 3. The attempt at a solution: I assume that the solution for the ZSR response needs to be for the initial condition Vc(t0)=0 or correct me if that's should be Vc(0)=0. I would appreciate any help, thanks a lot.