\[ 3 y(x) y'(x)-3 y'(x)^2+y(x) y''(x)-y(x)^2=0 \] ✓ Mathematica : cpu = 0.120968 (sec), leaf count = 25
\[\left \{\left \{y(x)\to \frac {c_2 e^x}{\sqrt {1-2 e^{x+c_1}}}\right \}\right \}\] ✓ Maple : cpu = 0.403 (sec), leaf count = 68
\[ \left \{ y \left ( x \right ) ={\frac {\sqrt {2}}{2\,{{\rm e}^{x}}{\it \_C1}-2\,{\it \_C2}}\sqrt { \left ( {{\rm e}^{x}}{\it \_C1}-{\it \_C2} \right ) {{\rm e}^{2\,x}}}},y \left ( x \right ) =-{\frac {\sqrt {2}}{2\,{{\rm e}^{x}}{\it \_C1}-2\,{\it \_C2}}\sqrt { \left ( {{\rm e}^{x}}{\it \_C1}-{\it \_C2} \right ) {{\rm e}^{2\,x}}}} \right \} \]