\[ y''(x)=-\frac {y(x)}{(a x+b)^4} \] ✓ Mathematica : cpu = 0.166022 (sec), leaf count = 49
\[\left \{\left \{y(x)\to e^{-\frac {i}{a (a x+b)}} (a x+b) \left (c_2+c_1 e^{\frac {2 i}{a (a x+b)}}\right )\right \}\right \}\]
✓ Maple : cpu = 0.073 (sec), leaf count = 39
\[ \left \{ y \left ( x \right ) = \left ( ax+b \right ) \left ( {\it \_C2}\,\cos \left ( {\frac {1}{a \left ( ax+b \right ) }} \right ) +{\it \_C1}\,\sin \left ( {\frac {1}{a \left ( ax+b \right ) }} \right ) \right ) \right \} \]