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Nov 2021 p33 q11
1933
\(The complex number -\sqrt{3} + i is denoted by u.\)
\((a) Express u in the form re^{i\theta}, where r > 0 and -\pi < \theta \leq \pi, giving the exact values of r and \theta.\)
(b) Hence show that u^6 is real and state its value.
(c) (i) On a sketch of an Argand diagram, shade the region whose points represent complex numbers z satisfying the inequalities 0 \leq \arg(z - u) \leq \frac{1}{4}\pi and \text{Re } z \leq 2.
(ii) Find the greatest value of |z| for points in the shaded region. Give your answer correct to 3 significant figures.
Solution
\((a) The modulus r of u = -\sqrt{3} + i is calculated as:\)
(c)(i) On the Argand diagram, draw half-lines from -\sqrt{3} + i at angles 0 and \frac{1}{4}\pi. Also, draw the vertical line x = 2. Shade the region bounded by these lines.
(c)(ii) The greatest value of |z| occurs at the intersection of the line x = 2 and the boundary of the shaded region. Calculate |z| at this point to find the maximum value:
\(The maximum distance from the origin to the line x = 2 is \sqrt{(2 - (-\sqrt{3}))^2 + 1^2} = 5.14.\)