The circumcentre of a triangle ABC is O. If ∠ BAC =

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The circumcentre of a triangle ABC is O. If ∠ BAC = 85° and ∠ BCA = 75°, then the value of ∠ OAC is

1. 40°
2. 60°
3. 70°
4. 90°

Correct Option: C

According to question , we draw a figure of triangle ABC and O is the circumcentre of a triangle ABC

Given , ∠BAC = 85°
∴ ∠BOC = 2 × 85° = 170°
⇒ ∠OBC = ∠OCB = 5°
∴ ∠OCA = ∠OAC = 75° – 5° = 70°