The circumcentre of a ΔABC is O. If BAC = 70° and BCA = 80°, then the measure of OAC is equal to:
Show answer & explanation
Correct answer: C
Explanation
The correct answer is Option 3 i.e. 60°.
∠ABC = 180° - (70° + 80°) = 30°
∠BOC = 2 × ∠BAC = 140° (central angle theorem)
In ΔBOC (isosceles), ∠OBC = ∠OCB = 20°
∠OCA = 80° - 20° = 60°
In ΔOAC (isosceles), ∠OAC = ∠OCA = 60°