The problem ask me to find the tension on a capacitor after a switch has been opened. I have everything in terms of equations in s-domain and I'm sure they aren't wrong because I checked on the book. My unique problem is to understand a certain passage necessary to find the voltage knowing the current. I found I(s) and I know v(0)/s of the capacitor. Then I just used this relation to find V(s) and compute its value in time: I(s)=C (sV(s)-v(0)). Here I solved for V(s) and I got the wrong answer. In fact, the book uses a different equation, actually just I sign changes, the following: V(s)= (1/sC) I(s) - v(0)/s. The first thing I thought was it was a Typing error, but checking other exercises showed it wasn't. So, my question is: why do we use it?