\[ -a y(x)-b+y''(x)^2=0 \] ✓ Mathematica : cpu = 1.43355 (sec), leaf count = 119
\[\left \{\text {Solve}\left [\frac {(a y(x)+b)^2 \, _2F_1\left (\frac {1}{2},\frac {2}{3};\frac {5}{3};-\frac {4 (b+a y(x))^{3/2}}{3 a c_1}\right ){}^2}{a^2 c_1}=\left (c_2+x\right ){}^2,y(x)\right ],\text {Solve}\left [\frac {(a y(x)+b)^2 \, _2F_1\left (\frac {1}{2},\frac {2}{3};\frac {5}{3};\frac {4 (b+a y(x))^{3/2}}{3 a c_1}\right ){}^2}{a^2 c_1}=\left (c_2+x\right ){}^2,y(x)\right ]\right \}\] ✓ Maple : cpu = 0.8 (sec), leaf count = 173
\[ \left \{ \int ^{y \left ( x \right ) }\!{a\sqrt {3}{\frac {1}{\sqrt {a \left ( 4\,{\it \_a}\,\sqrt {a{\it \_a}+b}a+4\,b\sqrt {a{\it \_a}+b}-{\it \_C1} \right ) }}}}{d{\it \_a}}-x-{\it \_C2}=0,\int ^{y \left ( x \right ) }\!-3\,{\frac {a}{\sqrt {-12\, \left ( \left ( a{\it \_a}+b \right ) ^{3/2}-{\it \_C1}/4 \right ) a}}}{d{\it \_a}}-x-{\it \_C2}=0,\int ^{y \left ( x \right ) }\!3\,{\frac {a}{\sqrt {-12\, \left ( \left ( a{\it \_a}+b \right ) ^{3/2}-{\it \_C1}/4 \right ) a}}}{d{\it \_a}}-x-{\it \_C2}=0,\int ^{y \left ( x \right ) }\!-{a\sqrt {3}{\frac {1}{\sqrt {a \left ( 4\,{\it \_a}\,\sqrt {a{\it \_a}+b}a+4\,b\sqrt {a{\it \_a}+b}-{\it \_C1} \right ) }}}}{d{\it \_a}}-x-{\it \_C2}=0,y \left ( x \right ) =-{\frac {b}{a}} \right \} \]