ECZ 2021 · O-Level Paper 1 — Circle Theorems
The points A, B, C and D are on the circumference of a circle centre O, such that angle AOC = 126°. AO is parallel to DC and angle OCB = 33°. Find (c) BAO.
- A. 30°
- B. 27°
- C. 33°
- D. 57°
Verified working — step 1
Triangle OBC is isosceles (OB = OC), so angle OBC = angle OCB = 33° and angle BOC = 180° − 2(33°) = 114°; the inscribed angle BAC = ½ × 114° = 57°. Triangle OAC is isosceles (OA = OC) with angle AOC = 126°, so angle OAC = 180° − 126°2= 27°. Therefore angle BAO = angle BAC − angle OAC = 57° − 27° = …The full step-by-step working and final answer are included with Premium — checked against ECZ marking standards.
Original examination question © Examinations Council of Zambia. Worked solution and commentary © G12 Titan — not to be reproduced without permission.
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