1. The problem statement, all variables and given/known data i tried to put all data in the image . http://img136.imageshack.us/img136/7443/photokg6.th.jpg [Broken] in the initial situation K was closed.in T = 0 ,K was opened. give the differenciel equation of the courant. 3. The attempt at a solution (R+r)*i + L (di)/(dt) = 0 . my problem is that i don't know if we have to put (R+r)*i or only r*i in the differentiel equation of the courant . thanks in advance for any help.