1. The problem statement, all variables and given/known data Differentiate V0 - iR - q/C = 0 to prove that di/dt = -i/RC. 2. Relevant equations V0 - iR - q/C = 0 ^ derived from previous question for a circuit that had one battery with emf V0, a resistor of resistance R and a capacitor of capacitance C (all in series). di/dt = -i/RC 3. The attempt at a solution V0 - iR - q/C = 0 V0 - (dq/dt)R - q/C = 0 V0C - (dq/dt)RC - q = 0 (dq/dt)RC = V0C - q d/dt((dq/dt)RC) = d/dt(V0C - q) RC(d/dt(dq/dt) = -dq/dt RC(di/dt) = -i di/dt = -i/RC ^ not sure if my maths makes sense (not very good at doing dif/integration when there are multiple variables). I did get the "answer" (which is easy, since its given), but obviously the method's what matters. Thanks a lot!