ECZ 2014 · O-Level Paper 1 — Similarity and Congruency
In the figure, ABCDE is part of a regular polygon. AC and BD meet at X, angle BXC = 140° and angle BDE = 120°. Find the number of sides of this polygon.
- A. 7
- B. 8
- C. 10
- D. 9
Verified working — step 1
Let the interior angle be I. Triangles ABC and BCD are isosceles with apex angle I, so angle ACB = angle DBC = 180° − I2. In triangle BXC these two base angles plus 140° make 180°, which gives 180° − I + 140° = 180°, so I = 140°. Then (n − 2) × 180°/n = 140° gives 40n = 360 and n = …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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