Evaluate : `int " sec"^(2) " 3x dx "`

Explanation

To evaluate the integral \( \int \sec^2(3x) \, dx \), we can follow these steps:

### Step 1: Substitution
Let \( t = 3x \). Then, differentiate both sides:
\[ dt = 3 \, dx \quad \Rightarrow \quad dx = \frac{dt}{3} \]

...