Find the values of `cospi/8`

Explanation

To find the value of \( \cos \frac{\pi}{8} \), we can use the double angle formula for cosine. Here’s a step-by-step solution:

### Step 1: Use the Cosine Double Angle Formula
The double angle formula for cosine states:
\[ \cos 2\theta = 2\cos^2 \theta - 1 \]
From this, we can derive:
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