Solution

ID: past-exam-of-the-mathematics-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2011/paper-1/4/a/solution

The distance from the origin is . The direction angle, measured counterclockwise from the positive horizontal axis, is modulo . Thus the path is an Archimedean spiral, turning clockwise through two complete revolutions as its radius decreases linearly from to zero.
It starts at , reaches at , crosses at , returns to the positive vertical axis at when , and ends at the origin when . These crossings fix both the scale and direction of the sketch.
Figure 1.
Two clockwise inward turns of the spiral, with time-direction arrows and selected axis crossings
. Details.

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