1
\(y'' = \sin y\), \(y(0) = \frac\pi2\), \(y'(0) = \sqrt 2\).
2
\(2(2a-y)y'' = y'^2\).
3
\(yy''=y'^2-y^2\) : poser \(z=y'/y\).
\(y'' = \sin y\), \(y(0) = \frac\pi2\), \(y'(0) = \sqrt 2\).
\(2(2a-y)y'' = y'^2\).
\(yy''=y'^2-y^2\) : poser \(z=y'/y\).