Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2003/ia/paper-2/1d/ii/solution

For , the separated integral is
Inverting gives
The upper branch has , where decreases towards as . The lower branch has , where decreases to as . These are separate maximal intervals: the pole is not part of a solution. For the domain , a lower-branch initial value below necessarily reaches that pole in finite positive . The direction field sketch above displays both exterior branches and a central hyperbolic tangent branch.

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