It's not an homework but a resolution of an equation in my course I would like to understand.

I'm not sure what happens there.
on the point a) I don't get the transition to q1, I don't get where the K comes from nor the exponential nor even q1.

 

You picture isn't showing. Try attaching it to your post. Use the Go Advanced button and then the Manage Attachments option down below.

 

Does it work now ? because I saw the picture on my end.

 

https://www.google.com/search?q=differential+equation+charge+capacitor See if this search can give you a push in the correct direction.

 

Does it work now ? because I saw the picture on my end.

It's showing, but I don't read French. Sorry.

 

Do you know how to do integration?

http://www.mathsisfun.com/calculus/integration-definite.html

 

It's showing, but I don't read French. Sorry.

Yes you are correct differential equations are much harder to solve then written in French