2020 SJI P1 Q9

2020 SJI P1 Q9

IB Year 5 | Grade 11
17 marks

Suppose \(z=\dfrac{4\sqrt2\,\mathrm{i}}{\sqrt6+\sqrt2\,\mathrm{i}}\), where \(\mathrm{i}^2=-1\).

  1. Show that \(z=1+\sqrt3\,\mathrm{i}\).[2]
  2. Hence, find in terms of \(n\),[4]
    1. \(\arg(z^n)\)
    2. \(|z^n|\)
  3. If \(w^2=z\), find the possible values of \(w\), leaving your answer in the form \(r\mathrm{e}^{\mathrm{i}\theta}\) where \(r>0\) and \(\theta\in(-\pi,\pi]\).[4]

Let \(z^n=r\big(\mathrm{f}(n)+\mathrm{i}\,\mathrm{g}(n)\big)\) for all \(n\in\mathbb Z^+\), where \(\mathrm{f}\) and \(\mathrm{g}\) are trigonometric functions of \(n\) and \(r=|z^n|\).

  1. Find \(\mathrm{f}(1)\), \(\mathrm{f}(2)\) and \(\mathrm{f}(3)\).[4]
  2. Calculate the product of the first \(12\) values of \(\mathrm{f}(n)\), that is, evaluate \[\mathrm{f}(1)\times\mathrm{f}(2)\times\mathrm{f}(3)\times\cdots\times\mathrm{f}(11)\times\mathrm{f}(12).\][3]

Solution:

Solution locked

Sign in to view the step-by-step solution

Similar questions are unavailable for this question.
Answer:(a) \(z=1+\sqrt3\,\mathrm{i}\) (b)(i) \(\arg(z^n)\equiv\dfrac{n\pi}3\pmod{2\pi}\), (ii) \(2^n\) (c) \(\sqrt2\,\mathrm{e}^{\mathrm{i}\pi/6},\ \sqrt2\,\mathrm{e}^{-5\mathrm{i}\pi/6}\) (d) \(\dfrac12,-\dfrac12,-1\) (e) \(\dfrac1{256}\)

Need help? Join our JC Math tuition classes.

Learn more