Step 1: Use trigonometric identity
Rewrite (\sin 7x = \sin(9x - 2x)).
(\sin(9x - 2x) = \sin 9x \cos 2x - \cos 9x \sin 2x).
Step 2: Split the fraction
(\int \frac{\sin 9x \cos 2x}{\cos 9x \cos 2x} , dx - \int \frac{\cos 9x \sin 2x}{\cos 9x \cos 2x} , dx).
(\int \tan 9x , dx - \int \tan 2x , dx).
Step 3: Integrate
(\frac{1}{9} \ln|\sec 9x| - \frac{1}{2} \ln|\sec 2x| + c).
Final Answer: (C)