Find the principal value of: `cos^(-1)(-1/(sqrt(2)))`

Explanation

To find the principal value of \( \cos^{-1}\left(-\frac{1}{\sqrt{2}}\right) \), we can follow these steps:

### Step 1: Use the property of inverse cosine
We know from the properties of inverse trigonometric functions that:
\[ \cos^{-1}(-x) = \pi - \cos^{-1}(x) \]
This means we can express \( \cos^{-1}\left(-\frac{1}{\sqrt{2}}\right) \) in terms of \( \cos^{-1}\left(\frac{1}{\sqrt{2}}\right) \).
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