ECZ 2015 · O-Level Paper 1 — Trigonometry
In the diagram, BCD is a straight line, AB = 12 cm, AC = 13 cm and angle ABC = 90°. Find, as a fraction, cos angle ACD.
- A. −513
- B. 513
- C. −1213
- D. 1213
Verified working — step 1
By Pythagoras, BC = √(13² − 12²) = 5 cm, so cos angle ACB = 513. Angle ACD = 180° − angle ACB (angles on the straight line BCD), and cos(180° − θ) = …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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