$ R_{n} = r \cdot q \cdot \dfrac{q^{n} \ - \ 1}{q \ - \ 1} \quad R_{n} = r \cdot \dfrac{q^{n} \ - \ 1}{q \ - \ 1} $

$ r = \frac{R_{n} \cdot \ (q \ - \ 1)}{q \ \cdot \ (q^{n} \ - \ 1)} \quad r = \frac{R_{n} \ \cdot \ (q \ - \ 1)}{q^{n} \ - \ 1} $

$ n = \dfrac{ln[\frac{R_{n} \ \cdot \ (q \ - \ 1)}{r \ \cdot \ q}\ + \ 1]}{ln \ q} \quad n = \frac{ln[\dfrac{R_{n} \ \cdot \ (q \ -\ 1)}{r} \ + \ 1]}{ln \ q} $