okay, here is my first math realated stupid question!
I tried to imagine i am design a circuit, that has as intput a 50Hz square wave, and swings from -2V to 2V. taking the initial condition : Vout and Vin = 0 at t = 0. i fixed the value of C to 10nF, and put V= 2V, t = 10ms and found the last unknown which was R = -100Kohm..!!
now, i know that if i used Vout = -2V instead of +2v, i would have got a logical +100Kohm... but what is the meaning of that negative sign?
i think i got the essential parts of the idea... but i hate those litle things that feels like a splinter in my mind!