Solution

ID: past-exam-of-the-mathematics-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2013/paper-1/13/b/solution

On a branch with , the given derivative is nonzero wherever the original equation is defined, so use inverse-function linearization of a first-order equation and regard as a function of :
The integrating factor gives
Thus the nonzero solutions are given implicitly by
Each branch must also retain ; at those excluded points the original right-hand side is undefined and the inverse graph cannot represent a regular . Differentiating the implicit equation gives , equal to the required quotient wherever these restrictions hold.
The additional solution , on any interval avoiding , was lost when dividing by and must be included. It is not defined through the point in the original equation.

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