2023 VJC Promo Q7

2023 VJC Promo Q7

10 marks
Promo

Do not use a calculator in answering this question.

  1. One of the roots of the equation \(3{{x}^{3}}+p{{x}^{2}}+qx+3=0\), where \(p\) and \(q\) are real, is \(1+\sqrt{2}\,\mathbf{i}\).
    Find the other roots and the values of  \(p\) and \(q\).[5]
  2. The complex numbers \(w\) and \(z\), with \(\left| w \right|<\left| z \right|\), satisfy the simultaneous equations
    \(w{{z}^{*}}=3-\mathbf{i}\) and \(w+{{z}^{*}}=2-\mathbf{i}\).
    Find \(w\) and \(z\).[5]

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Answer:(a) Other roots \(1-\sqrt2\,\mathrm{i}\) and \(-\dfrac13\), \(p=-5\), \(q=7\) (b) \(w=1+\mathrm{i}\), \(z=1+2\mathrm{i}\)

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