Prove that : `cos(pi/7)cos((2pi)/7) cos((3pi)/7)=1/8`

Explanation

To prove that \( \cos\left(\frac{\pi}{7}\right) \cos\left(\frac{2\pi}{7}\right) \cos\left(\frac{3\pi}{7}\right) = \frac{1}{8} \), we will follow a series of steps using trigonometric identities.

### Step 1: Start with the left-hand side
We begin with the expression we want to prove:
\[ LHS = \cos\left(\frac{\pi}{7}\right) \cos\left(\frac{2\pi}{7}\right) \cos\left(\frac{3\pi}{7}\right) \]

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