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 (a) ADC.
- A. 63°
- B. 126°
- C. 117°
- D. 54°
Verified working — step 1
The central angle AOC = 126° stands on arc AC, so the inscribed angle ABC on that same arc = 126°/2 = 63°. ABCD is a cyclic quadrilateral, so opposite angles ADC and ABC are supplementary: ADC = 180° − 63° = …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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