$\begin{array}{l}{\text { (a) Fibonacci posed the following problem: Suppose that }} \\ {\text { rabbits live forever and that every month each pair }} \\ {\text { produces a new pair which becomes productive at age }} \\ {2 \text { months. If we start with one newborn pair, how many }}\end{array}$
$\begin{array}{l}{\text { pairs of rabbits will we have in the } n \text { th month? Show that }} \\ {\text { the answer is } f_{n} \text { , where }\left\{f_{n}\right\} \text { is the Fibonacci sequence }} \\ {\text { defined in Example } 3(\mathrm{c})}\end{array}$
$\begin{array}{l}{\text { (b) Let } a_{n}=f_{n+1} / f_{n} \text { and show that } a_{n-1}=1+1 / a_{n-2}} \\ {\text { Assuming that }\left\{a_{n}\right\} \text { is convergent, find its limit. }}\end{array}$