Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-oxford/undated/prelims/mathematics-iii-resit/1/a/solution

Divide by . The product rule turns the linear ordinary differential equation into
Equivalently, is an integrating factor after division by . An antiderivative gives . The initial condition at gives , hence
Its derivative is , so substitution gives , and . Every solution of a differential equation has the integrated form above, and the initial condition fixes its only constant. This agrees with the uniqueness theorem for ordinary differential equations on the stated interval.

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