\[ \boxed { \left ( {a}^{2} \left ( y \left ( x \right ) \right ) ^{2}-{b}^{2} \right ) \left ( {\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left ( x \right ) \right ) ^{2}-2\,{a}^{2}y \left ( x \right ) \left ( {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) \right ) ^{2}{\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left ( x \right ) + \left ( {a}^{2} \left ( {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) \right ) ^{2}-1 \right ) \left ( {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) \right ) ^{2}=0} \]
Mathematica: cpu = 0 (sec), leaf count = 0 \[ \text {Hanged} \]
Maple: cpu = 2.465 (sec), leaf count = 145 \[ \left \{ y \left ( x \right ) ={\it \_C1},y \left ( x \right ) ={b \left ( {{\rm e}^{{\frac {{\it \_C2}+x}{b}\sqrt {{{\it \_C1}}^{2}{a}^{2}-1}}}} -{\it \_C1} \right ) {\frac {1}{\sqrt {{{\it \_C1}}^{2}{a}^{2}-1}}}},y \left ( x \right ) ={\frac {b}{a}\tan \left ( {\frac {{\it \_C1}-x}{ab} \sqrt {{a}^{2}}} \right ) {\frac {1}{\sqrt { \left ( \tan \left ( {\frac {{\it \_C1}-x}{ab}\sqrt {{a}^{2}}} \right ) \right ) ^{2}+1}}}},y \left ( x \right ) =-{\frac {b}{a}\tan \left ( {\frac {{\it \_C1}-x}{ab} \sqrt {{a}^{2}}} \right ) {\frac {1}{\sqrt { \left ( \tan \left ( {\frac {{\it \_C1}-x}{ab}\sqrt {{a}^{2}}} \right ) \right ) ^{2}+1}}}} \right \} \]