Evaluate `int1/(1+cos3x)dx`

Explanation

To evaluate the integral \( \int \frac{1}{1 + \cos 3x} \, dx \), we can follow these steps:

### Step 1: Multiply and Divide by \( 1 - \cos 3x \)
We start by multiplying and dividing the integrand by \( 1 - \cos 3x \):
\[ \int \frac{1}{1 + \cos 3x} \, dx = \int \frac{1 - \cos 3x}{(1 + \cos 3x)(1 - \cos 3x)} \, dx \]

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