Discharging:

$$ \begin{aligned}

\frac{q(t)}{C} & =\frac{Q_{\text {max }}}{C} e^{-\frac{t}{\tau}} \

V(t) & =V_{\text {max }} e^{-\frac{t}{\tau}} \

\ln V & =\ln \left(V_{\text {max}} e^{-\frac{t}{\tau}}\right) \

& =\ln \left(e^{-\frac{t}{\tau}}\right)+\ln \left(V_{\text {max }}\right) \

\ln V & =-\frac{t}{\tau}+\text { Constant }

\end{aligned} $$

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