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Answer each of the following questions in one word or one sentence or as per exact requirement of the question:
Write the principal value of cos–1(cos 680°).
Given cos-1 (cos 680°)
= cos-1 (cos (720° - 40°))
= cos-1 (cos (2 × 360° - 40°))
= cos-1 (cos 40°)
= 40°
∴ cos-1 (cos 680°) = 40°