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Specialist Mathematics · Unit 2 · Complex numbers · The complex plane (the Argand plane)

Understand and use multiplication by a complex number as a linear transformation in the complex plane.

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Question 1

The table below shows four complex numbers and their images under a linear transformation T defined by T(z) = wz, where w is a fixed complex number. Determine the values of p, q, and r, and show that w = √2 cis(5π/12).

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Question 2

Consider the complex number \(w = 1 + i\). a) Determine the modulus and argument of \(w\), expressing the argument in exact form. b) The complex number \(z = 3 - i\) is multiplied by \(w\) to give \(z' = wz\). Use your results from part (a) to describe the geometric transformation that maps \(z\) to \(z'\) in the complex plane.

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Question 3

Consider the complex number \(w = \sqrt{3} + i\). a) Express \(w\) in modulus-argument form. (1 mark) b) The transformation \(T\) maps a complex number \(z\) to \(wz\). Use your result from part (a) to describe geometrically the effect of transformation \(T\) on any complex number \(z\) in the complex plane. (2 marks)

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Question 4

The complex number \(z = 2 + 3i\) is multiplied by \(w = \operatorname{cis}\left(\frac{\pi}{3}\right)\). Determine the modulus of the resulting complex number \(zw\).

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