ECZ 2013 · O-Level Paper 1 — Circle Theorems
A circle centre O passes through the points A, B, C and D. Angle AOC = 110 degrees and AO is parallel to BC. Find angle ABC.

- A. 55 degrees
- B. 110 degrees
- C. 125 degrees
- D. 145 degrees
Verified working — step 1
B lies on the major arc, so angle ABC stands on the reflex angle AOC = 360 - 110 = 250 degrees. The angle at the circumference is half the angle at the centre: 2502= …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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