\[ y(x) y''(x)-y'(x)^2+1=0 \] ✓ Mathematica : cpu = 0.176879 (sec), leaf count = 44
DSolve[1 - Derivative[1][y][x]^2 + y[x]*Derivative[2][y][x] == 0,y[x],x]
\[\left \{\left \{y(x)\to -e^{-c_1} \sinh \left (e^{c_1} (x+c_2)\right )\right \},\left \{y(x)\to e^{-c_1} \sinh \left (e^{c_1} (x+c_2)\right )\right \}\right \}\] ✓ Maple : cpu = 1.13 (sec), leaf count = 86
dsolve(diff(diff(y(x),x),x)*y(x)-diff(y(x),x)^2+1=0,y(x))
\[y \left (x \right ) = \frac {\left (-c_{1} {\mathrm e}^{\frac {2 x}{c_{1}}} {\mathrm e}^{\frac {2 c_{2}}{c_{1}}}+c_{1}\right ) {\mathrm e}^{-\frac {c_{2}}{c_{1}}} {\mathrm e}^{-\frac {x}{c_{1}}}}{2}\]