ECZ 2015 · O-Level Paper 1 — Circle Theorems
In the diagram, A, B, C and D are points on the circumference of a circle with centre O. ADE and BCE are straight lines, angle CED = 28° and angle BCA = 43°. Find angle CDB.
- A. 75°
- B. 43°
- C. 15°
- D. 105°
Verified working — step 1
Angles on the straight line BCE give angle ACE = 180° − 43° = 137°, so in triangle ACE angle CAE = 15°, which is angle DAC. BD is a diameter, so angle DAB = 90°. Then angle CAB = 90° − 15° = 75°, and angle CDB = angle CAB = …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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