What is the Differential Equation for the Current in an Auto Induction Circuit?

[toetoe]

Homework Statement

i tried to put all data in the image .

http://img136.imageshack.us/img136/7443/photokg6.th.jpg

in the initial situation K was closed.in T = 0 ,K was opened.

give the differenciel equation of the courant.

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.

 

[toetoe]

by the way,if there is something not clear in the data of the problem ,i will be happy to explain it.

 

[toetoe]

does nobody know the solution?

 

[toetoe]

no answer !:(