ECZ 2025 · GCE Paper 1 — Circle Theorems
Use the diagram. A, B, C, D and E lie on a circle with centre O. angle ADB = 18°, angle EAD = 31°, and BC = CD. Find angle ADC.
- A. 45°
- B. 18°
- C. 49°
- D. 63°
Verified working — step 1
B, O and D are collinear, so BD is a diameter and angle BCD = 90° (angle in a semicircle). Since BC = CD, triangle BCD is an isosceles right-angled triangle, so angle BDC = 180° − 90°2= 45°. Then angle ADC = angle ADB + angle BDC = 18° + 45° = …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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