Solution

ID: past-exam-of-the-mathematical-methods-i-course-of-the-university-of-oxford/2015-resit/1/iii/solution

For , the equation becomes . Its right side must be nonnegative. Squaring then gives , whose points already have , so no extraneous branch has been introduced:
This is a parabola opening along the positive real axis, with vertex , focus and directrix . The original modulus equation equates distance from the focus with distance from that directrix.
Figure 1.
The three complex-plane loci: a single point, four fourth roots, and a right-opening parabola
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