Solution

ID: past-exam-of-the-mathematical-methods-i-course-of-the-university-of-oxford/2017-resit/3/solution

The real logarithm requires . The identically zero function is a solution and must be retained before dividing by . For a nonzero solution, divide by and make the Bernoulli differential equation substitution . This gives
Integration yields . Consequently
with each nonzero branch restricted to an interval where its denominator is nonzero. The right-hand side of the first-order equation is locally Lipschitz in for , so a nonzero solution cannot cross the zero solution at a finite positive .

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