c
\(\begin{array}{l}
\,{\left( 5 \right)^2}\,\, + \;\,{\left( {12} \right)^2}\,\, = \,\,{\left( {13} \right)^2}\\
 \Rightarrow \,\,\cos \theta \,\, = \,\,\frac{{12}}{{13}}\,\,\\ \therefore \,\,\theta \,\, = \,\,{\cos ^{ - 1}}\,\,\left( {\frac{{12}}{{13}}} \right)
\end{array}\)