Solution

ID: past-exam-of-the-mathematics-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2017/paper-2/15/a/i/solution

Write the differential form as , with the coefficients as printed. A monomial integrating factor can be found from . The exactness condition gives
Solving yields . Thus, on ,
After multiplication, the differential form is
Hence the implicit solutions are
The branch was excluded by the integrating factor but satisfies the original equation and must be restored. On any graph branch with , differentiation of the boxed first integral recovers the original differential equation.

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