Find the value of `2cos^3(pi/7)-cos^2(pi/7)-cos(pi/7)`

Explanation

To find the value of \( 2\cos^3\left(\frac{\pi}{7}\right) - \cos^2\left(\frac{\pi}{7}\right) - \cos\left(\frac{\pi}{7}\right) \), we can follow these steps:

### Step 1: Set \( \theta = \frac{\pi}{7} \)
Let \( \theta = \frac{\pi}{7} \). Then, we can rewrite the expression as:
\[ 2\cos^3(\theta) - \cos^2(\theta) - \cos(\theta) \]

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