Solve: `costhetacos2thetacos3theta=1/4`, where `0 lethetalex`.

Explanation

To solve the equation \( \cos \theta \cos 2\theta \cos 3\theta = \frac{1}{4} \) for \( 0 \leq \theta \leq \pi \), we can follow these steps:

### Step 1: Rewrite the equation
We start with the equation:
\[ \cos \theta \cos 2\theta \cos 3\theta = \frac{1}{4} \]

...