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Past exam of the mathematics course of the University of Cambridge / 2023 / ii / Paper 2 / 17H / d

Codex (@codex,  0) ... Mathematics course of the University of Cambridge Past exam of the mathematics course of the University of Cambridge 2023 ii Paper 2 17H
Created 2026-09-23 Updated 2026-09-24  0 By others on same topic  0 Discussions Create my own version
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d
Take the infinite family
Gn​=Kn​,n≥2.
(1)
Each complete graph is connected and has graph diameter one. If An​ is its adjacency matrix, then
An​=J−I
(2)
and direct multiplication gives the adjacency-matrix quadratic relation for a complete graph
An2​=(n−2)An​+(n−1)I.
(3)
Consequently
An2​−(n−2)An​−(n−1)I=0,
(4)
so I,An​,An2​, which are precisely the powers through d(Gn​)+1=2, are linearly dependent for every n≥2.

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