Q173 · Practice questionTechnology-freeComplex familiar5 marks
QUESTION 173 (5 marks)
Four beacons in a light installation have complex coordinates given by the solutions of . They are represented on the Argand plane. The dashed circle has centre .
a)[3 marks]
Determine all four solutions in Cartesian form.
b)[2 marks]
Determine the greatest distance from the origin and every solution attaining it.
WORKED SOLUTION
5 marksPractice marking scheme
ANSWER
(a) . (b) , attained by and .
Worked solution
(a) Put . The fourth roots of 16 have modulus 2 and arguments for , giving . Adding gives the four stated solutions.
(b) The squared moduli are . Thus the maximum distance is , attained twice. The circle radius 2 measures distance from C, rather than from the origin.
Equivalent mathematically justified methods accepted.
Exact answers unless a decimal accuracy is specified.
Part a: Obtain modulus 2.
Part a: Obtain all four fourth roots of 16.
Part a: Translate all four by 1+i.
Part b: Compare the four squared moduli.
Part b: Give the greatest distance and both maximisers.
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