2019 TJC P1 Q8

2019 TJC P1 Q8

12 marks
Prelims

Do not use a calculator in answering this question.

The complex numbers \(z\) and \(w\) are given by \(z=\frac{{{\left( 1+\mathbf{i} \right)}^{4}}}{{{\left( 1-\mathbf{i} \right)}^{2}}}\) and \(w=\frac{8}{{{\left( \sqrt{3}+\mathbf{i} \right)}^{2}}}\).

  1. Express \(z\) and \(w\) in polar form \(r\left( \cos \theta +\mathbf{i}\sin \theta \right)\), where \(r>0\) and \(-\pi <\theta \le \pi \). Give \(r\) and \(\theta \) in exact form.[4]
  2. Given that \({{z}^{2}}\), \(w\) and \({{w}^{*}}\) are the roots of the equation \({{x}^{3}}+b{{x}^{2}}+cx+d=0\) where \(b\), \(c\) and \(d\) are real values, find the equation.[3]
  3. Sketch on an Argand diagram with origin \(O\), the points \(P\), \(Q\) and \(R\) representing the complex numbers \(z\), \(w\) and \(z+w\) respectively.[2]
  4. By considering the quadrilateral \(OPRQ\) and the argument of \(z+w\), deduce that
    \(\tan \frac{5\pi }{12}=2+\sqrt{3}\).[3]

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Answer:\(z = 2e^{-\mathrm{i}\frac{\pi}{2}}\), \(w = 2e^{-\mathrm{i}\frac{\pi}{3}}\); \(x^3 + 2x^2 - 4x + 16 = 0\); \(\tan\left(\frac{5\pi}{12}\right) = 2 + \sqrt{3}\)

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