ECZ 2021 · GCE Paper 1 — Trigonometry
The diagram shows triangle ABC in which AB = 5cm and AC = 13cm. Angle ABC = 90° and BC is produced to D. Find the value of cos ACD.
- A. 1213
- B. −1213
- C. −513
- D. 512
Verified working — step 1
By Pythagoras, BC = √(13² − 5²) = √144 = 12, so cos ACB = 1213. Since D lies on BC produced, angle ACD = 180° − angle ACB, and the cosine of a supplementary angle changes sign: cos ACD = …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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