Write the principal value of `cos^(-1)[cos(680^@)]`

Explanation

To find the principal value of \( \cos^{-1}[\cos(680^\circ)] \), we can follow these steps:

### Step 1: Understand the periodicity of the cosine function
The cosine function is periodic with a period of \( 360^\circ \). This means:
\[ \cos(680^\circ) = \cos(680^\circ - 360^\circ) = \cos(320^\circ) \]

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