2026 CCHY P2 Q7

2026 CCHY P2 Q7

Secondary 4
8 marks

Given that \(\cos x=-\dfrac45\) and \(\tan x>0\), find the exact value of

  1. \(\sin2x\),[2]
  2. \(\cos\dfrac x2\),[3]
  3. \(\cot\dfrac x2\).[3]

Solution:

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Answer:(a) \(\dfrac{24}{25}\). (b) \(\pm\dfrac{\sqrt{10}}{10}\) as written; intended \(-\dfrac{\sqrt{10}}{10}\) for \(180^\circ<x<270^\circ\). (c) \(-\dfrac13\).

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