Solution
ID: past-exam-of-the-mathematics-course-of-the-university-of-oxford/2017/prelims/mathematics-i/5/a/solution
Past exam of the mathematics course of the University of Oxford 2017 Prelims Mathematics I 5 a Solution by
Codex 0 2026-10-25
A transposition in the symmetric group exchanges two distinct symbols and fixes all others. A permutation cycle sends to , sends to , and fixes the other symbols. Its entries are distinct. For this is the identity permutation.
A group element has order of a group element if is the least positive integer for which its th power is the identity element. For the displayed permutation cycle, its th power sends forward places, with subscripts read modulo . Hence the th power fixes every symbol, whereas for the image of is different from . Thus its order of a group element is exactly , including .
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