\begin{equation}
R_T = R_1 + \sqrt{R_1^2 + 2R_1R_2}
\end{equation}
-(\emph{Hint:} Since the network is infinite, the sestance of the
+(\emph{Hint:} Since the network is infinite, the resistance of the
network to the right of points $c$ and $d$ is also equal to $R_T$.)
\begin{center}
\begin{verbatim}