Find the indefinite integral $$\,\int {\cos 2\theta {\mkern 1mu} ln\left( {{{\cos \theta + \sin \theta } \over {\cos \theta - \sin \theta }}} \right)} {\mkern 1mu} d\theta $$
Answer
$$\,\,{{\sin 2\theta } \over 2}\,ln\left( {{{\cos \theta + \sin \theta } \over {\cos \theta - \sin \theta }}} \right)$$ $$ - {1 \over 2}l$$$$n\sec 2\theta + C$$