N2008 P2 Q3

N2008 P2 Q3

Junior College 2
11 marks
  1. The complex number \(w\) has modulus \(r\) and argument \(\theta\), where \(0<\theta<\frac12\pi\), and \(w^*\) denotes the conjugate of \(w\). State the modulus and argument of \(p\), where \(p=\frac w{w^*}\).[2]

Given that \(p^5\) is real and positive, find the possible values of \(\theta\).[2]

  1. The complex number \(z\) satisfies the relations \(|z|\leq6\) and \(|z|=|z-8-6\mathrm i|\).
    1. Illustrate both of these relations on a single Argand diagram.[3]
    2. Find the greatest and least possible values of \(\arg z\), giving your answers in radians correct to 3 decimal places.[4]

Solution:

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Answer:(a) Modulus 1, argument \(2\theta\); \(\theta=\pi/5,2\pi/5\). (b) \(4x+3y=25\), \(x^2+y^2\leq36\); greatest \(1.229\), least \(0.058\) radians.

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