## Calculus (3rd Edition)

$$\frac{R}{r}$$
Since we have for $R(t) =R$ $$P V = \frac{R}{r}\left(1-e^{-r T}\right)$$ Then for large $T$ \begin{align*} PV&=\lim_{T\to \infty }\frac{R}{r}\left(1-e^{-r T}\right)\\ &=\frac{R}{r} \end{align*}