# General solution of $yy'' - (y')^2 + y' = 0$

How do you derive the general solution of $$y y'' - (y')^2 + y' = 0$$ Thanks.

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Never mind. Solved.

Let $u = y'$. Then $y'' = u' = \frac{du}{dy}$ . $y' = \frac{du}{dy} . u$

Hence the equation is $$yu \cdot\frac{du}{dy} = u^2 - u$$ which is separable.

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Hint: Divide everything by $y^2$. Then use the identities $$\left(\dfrac{y'}y\right)'=\dfrac{y''y-(y')^2}{y^2}\qquad\text{and}\qquad\left(\dfrac1y\right)'=\dfrac{-y'}{y^2}.$$
Note that $y=0$ is a solution too. You may lose it after division. – Norbert Jan 2 '12 at 14:10