N2016 P2 Q4

N2016 P2 Q4

Junior College 2
12 marks
  1. Two loci in the Argand diagram are given by the equations \[|z-3-\mathrm i|=1\quad\text{and}\quad\arg z=\alpha,\quad\text{where}\hspace{0.5em}\tan\alpha=0.4.\] The complex numbers \(z_1\) and \(z_2\), where \(|z_1|<|z_2|\), correspond to the points of intersection of these loci.
    1. Draw an Argand diagram to show both loci, and mark the points represented by \(z_1\) and \(z_2\).[2]
    2. Find the two values of \(z\) which represent points on \(|z-3-\mathrm i|=1\) such that \(|z-z_1|=|z-z_2|\).[4]
    1. The complex number \(2-2\mathrm i\) is denoted by \(w\). By writing \(w\) in polar form \(r\mathrm e^{\mathrm i\theta}\), where \(r>0\) and \(-\pi<\theta\le\pi\), find exactly all the cube roots of \(w\) in polar form.[3]
    2. Find the smallest positive whole number value of \(n\) such that \(\arg(w^*w^n)=\frac12\pi\).[3]

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Answer:(a)(ii) \(z=3\pm2/\sqrt{29}+\mathrm i(1\mp5/\sqrt{29})\) (b)(i) \(\sqrt2\mathrm e^{-\mathrm i\pi/12},\sqrt2\mathrm e^{7\mathrm i\pi/12},\sqrt2\mathrm e^{-3\mathrm i\pi/4}\) (ii) \(7\).

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