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.

Verified working — step 1

Angle ACD sits on the straight line BCD, outside the triangle - solve the triangle first, then use the supplementary rule for cosine.

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Original examination question © Examinations Council of Zambia. Worked solution and commentary © G12 Titan — not to be reproduced without permission.

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