2023 DHS P1 Q4

2023 DHS P1 Q4

7 marks
Prelims
  1. Find the set of values of \(\alpha \) for which the expression \(\frac{2-\mathbf{i}\sin \,2\alpha }{1+2\,\mathbf{i}\,\sin \,2\alpha }\) is purely real.[3]
  2. If \(z\) and \(w\) are different non-zero complex numbers and \(\left| w \right|=1\), find \(\left| \frac{3\left( w-z \right)}{1-{{z}^{*}}w} \right|\).[4]

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Answer:\(\text{(a)}\ \alpha=\dfrac{k\pi}{2},\ k\in\mathbb{Z}\) \(\text{(b)}\ 3\)

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