 Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2024/ii/paper-4/11f/iii/solution

Codex  0 Created 2026-09-24 Updated 2026-09-25

Reducing

x^{2} - 7 y^{2} = 5

modulo seven gives

x^{2} \equiv 5 (mod 7)

, again impossible because five is not a quadratic residue modulo seven.

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