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Paper 1 · June 2011 · Trigonometry

In triangle ABCABC the sides BCBC, CACA and ABAB are aa, bb and cc respectively, and cot⁡C=accosec⁡B−cot⁡B\cot C = \dfrac{a}{c}\operatorname{cosec} B - \cot B. Given a=14.7a = 14.7 cm, c=17.3c = 17.3 cm and B=64.2°B = 64.2°, find angle CC correct to the nearest 0.1°0.1°.

A41.5°41.5°
B50.5°50.5°
C65.3°65.3°
D24.7°24.7°

Explanation

cot⁡C=14.717.3cosec⁡(64.2°)−cot⁡(64.2°)=0.9434×1.1108−0.4834=0.4604\cot C = \tfrac{14.7}{17.3}\operatorname{cosec}(64.2°) - \cot(64.2°) = 0.9434\times1.1108 - 0.4834 = 0.4604, so tan⁡C=2.172\tan C = 2.172 and C=65.3°C = 65.3°.

Derived from ZIMSEC Mathematics Paper 1, June 2011, Q6

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