Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-oxford/2021/prelims/mathematics-iv-resit/7/b/ii/solution

Back-substitute in the Euclidean algorithm to obtain an integer linear combination:
Multiplying by gives the particular solution of the linear Diophantine equation. Subtracting it from any other solution and dividing by gives
The integers and are coprime, so divides . Writing forces . Conversely these expressions satisfy the original equation for every integer . Thus all solutions of a linear Diophantine equation here are

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