N2012 P2 Q2

N2012 P2 Q2

Junior College 2
9 marks

The complex number \(z\) satisfies the equation \(|z-(7-3\mathrm i)|=4\).

  1. Sketch an Argand diagram to illustrate this equation.[2]
  2. Given that \(|z|\) is as small as possible,
    1. find the exact value of \(|z|\),[2]
    2. hence find an exact expression for \(z\), in the form \(x+\mathrm iy\).[2]
  3. It is given instead that \(-\pi<\arg z\le\pi\) and that \(|\arg z|\) is as large as possible. Find the value of \(\arg z\) in radians, correct to 4 significant figures.[3]

Solution:

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Answer:(ii)(a) \(\sqrt{58}-4\); (b) \(7-28/\sqrt{58}+\mathrm i(-3+12/\sqrt{58})\). (iii) \(-0.9579\) radians.

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