Answer each of the following questions in one word or one sentence or as per exact requirement of the question:

Find the value of .

Given cos^{-1} (cos 13π/6)

= cos^{-1} [cos (2π + π/6)]

= cos^{-1} (cos π/6)

= π/6

∴ cos^{-1} (cos 13π/6) = π/6

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