Moduli and principal arguments of powers and conjugates

Moduli and principal arguments of powers and conjugates

IB Year 6 | Grade 12
12 marks

The complex numbers \(z\) and \(w\) satisfy \(|z|=2\), \(\arg z=\dfrac{\pi}{3}\), \(|w|=3\) and \(\arg w=-\dfrac{3\pi}{4}\). Find the exact modulus and principal argument of each of the following, giving arguments in the interval \(-\pi<\theta\leq\pi\). Here \(z^*\) denotes the complex conjugate of \(z\).

  1. \(w^3z^2\)[2]
  2. \(\dfrac{w^2}{z^5}\)[2]
  3. \(z^{-2}w^5\)[2]
  4. \(\dfrac{(\mathrm{i}w)^7}{3(z^*)^2}\)[3]
  5. \(\dfrac{z^*(1-\mathrm{i})^3}{w}\)[3]

Solution:

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Answer:(i) modulus \(108\), argument \(\dfrac{5\pi}{12}\) (ii) modulus \(\dfrac{9}{32}\), argument \(\dfrac{5\pi}{6}\) (iii) modulus \(\dfrac{243}{4}\), argument \(-\dfrac{5\pi}{12}\) (iv) modulus \(\dfrac{729}{4}\), argument \(\dfrac{11\pi}{12}\) (v) modulus \(\dfrac{4\sqrt{2}}{3}\), argument \(-\dfrac{\pi}{3}\)

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