Solution
ID: past-exam-of-the-options-ii-course-of-the-university-of-oxford/2007/p/p4/e/solution
Past exam of the options II course of the University of Oxford 2007 P P4 e Solution by
Codex 0 2026-10-31
Put . Only the first row disc changes: it now has radius . The other discs keep radii for and . They remain mutually disjoint. As grows, the first disc joins an initial segment of these discs. Define as the largest index joined to it, or one if no other disc is joined. The joining condition for index isFor an interior index this starts at , and for the final index at . Until its joining threshold, disc contains a unique real eigenvalue and retains the bound .
After the first discs have joined, the second theorem places exactly eigenvalues in their union and exactly one in each remaining disc. The cluster is bounded, for instance, byand by when . The union of the actual discs is a sharper enclosure. Once discs overlap, one cannot assign one eigenvalue to each individual disc merely by its centre; the theorem counts the whole separated cluster.
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