2.23   ODE No. 23

\[ a y(x)^2-b+y'(x)=0 \] Mathematica : cpu = 0.0745175 (sec), leaf count = 43


\[\left \{\left \{y(x)\to \frac {\sqrt {b} \tanh \left (\sqrt {a} \sqrt {b} x+\sqrt {a} \sqrt {b} c_1\right )}{\sqrt {a}}\right \}\right \}\] Maple : cpu = 0.043 (sec), leaf count = 23


\[y \relax (x ) = \frac {\tanh \left (\sqrt {a b}\, \left (x +c_{1}\right )\right ) \sqrt {a b}}{a}\]

Hand solution

\begin {align*} y^{\prime }+ay^{2}-b & =0\\ \frac {dy}{dx} & =b-ay^{2} \end {align*}

Separable,\begin {align*} \frac {dy}{b-ay^{2}} & =dx\\ \int \frac {dy}{b-ay^{2}} & =\int dx \end {align*}

But \[ \int \frac {dy}{b-ay^{2}}=\frac {1}{\sqrt {ab}}\tanh ^{-1}\left (\sqrt {\frac {a}{b}}y\right ) \] Hence\begin {align*} \frac {1}{\sqrt {ab}}\tanh ^{-1}\left (\sqrt {\frac {a}{b}}y\right ) & =x+C\\ \tanh ^{-1}\left (\sqrt {\frac {a}{b}}y\right ) & =\sqrt {ab}\left ( x+C\right ) \\ \sqrt {\frac {a}{b}}y & =\tanh \left (\sqrt {ab}\left (x+C\right ) \right ) \\ y & =\sqrt {\frac {b}{a}}\tanh \left (\sqrt {ab}\left (x+C\right ) \right ) \end {align*}