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Find an implicit formula satisfied by solutions of y (1 – x2)1/2 y′ = x

Assume solutions of the equation

    \[ y \sqrt{1-x^2} y' = x \]

exist and find an implicit formula satisfied by these solutions.


This is a separable first order equation. We compute

    \begin{align*}  y \sqrt{1-x^2} y' = x && \implies && yy' &= \frac{x}{\sqrt{1-x^2}} \\[9pt]  && \implies && \int y \, dy &= \int \frac{x}{\sqrt{1-x^2}} \, dx \\[9pt]  && \implies && \frac{1}{2} y^2 &= -\sqrt{1-x^2} + C \\[9pt]  && \implies && y^2 + 2 \sqrt{1-x^2} &= C. \end{align*}

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