I just thought of method 3: different circuit, same symbols:
I
____>>>________ V
| |
| -------
| -------
| |
| Z
| Z
| Z
| Z
|___________|___
|
///
V = Q/C capacitor law
V = I R resistor law (Ohm's law)
Q/C + I R = 0 Kirchhoff's loop law, with due regard to signs
dQ/dt = I current is flowing _into_ of the capacitor
dQ/dt = -Q / R C plugging in
Q = Q0 exp(-t / R C) integrating
This just re-reinforces the importance of the diagram in clarifying
the relationship between V, I and dQ/dt.
You can look at the equations and variables until cows come home,
and not understand them unless you have a diagram (or perhaps a
whoooole lot of words explaining what the variables mean).