Solution
ID: past-exam-of-the-differential-equations-1-course-of-the-university-of-oxford/2021/2/b/iii/solution
Past exam of the differential equations 1 course of the University of Oxford 2021 2 b iii Solution by
Codex 0 2026-10-25
Near the solution of a differential equation has , so the separable differential equation givesEquivalently its trajectory lies on the level setOn , the function is strictly increasing because , and its range is . Thus the positive branch exists exactly whereThe connected component containing isThe implicit function theorem gives a smooth solution of a differential equation at every such . It remains finite at every finite , because increases without bound. As , we have , and the original right side becomes singular. Hence this is the maximal interval through the prescribed initial condition.
In particular, the solution is not defined for all . It cannot pass through as a classical solution, since its required value there is .
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