\[ 2 (y(x)-a) y''(x)+y'(x)^2+1=0 \] ✓ Mathematica : cpu = 0.298866 (sec), leaf count = 204
\[\left \{\left \{y(x)\to \text {InverseFunction}\left [-\sqrt {2} \left (\frac {1}{2} \sqrt {a-\text {$\#$1}} \sqrt {e^{2 c_1}-2 (a-\text {$\#$1})}-\frac {e^{2 c_1} \tan ^{-1}\left (\frac {\sqrt {2} \sqrt {a-\text {$\#$1}}}{\sqrt {e^{2 c_1}-2 (a-\text {$\#$1})}}\right )}{2 \sqrt {2}}\right )\& \right ]\left [c_2+x\right ]\right \},\left \{y(x)\to \text {InverseFunction}\left [\sqrt {2} \left (\frac {1}{2} \sqrt {a-\text {$\#$1}} \sqrt {e^{2 c_1}-2 (a-\text {$\#$1})}-\frac {e^{2 c_1} \tan ^{-1}\left (\frac {\sqrt {2} \sqrt {a-\text {$\#$1}}}{\sqrt {e^{2 c_1}-2 (a-\text {$\#$1})}}\right )}{2 \sqrt {2}}\right )\& \right ]\left [c_2+x\right ]\right \}\right \}\]
✓ Maple : cpu = 0.622 (sec), leaf count = 293
\[ \left \{ -\sqrt {- \left ( y \left ( x \right ) \right ) ^{2}+ \left ( 2\,a+{\it \_C1} \right ) y \left ( x \right ) -a \left ( {\it \_C1}+a \right ) }+\arctan \left ( {1 \left ( y \left ( x \right ) -a-{\frac {{\it \_C1}}{2}} \right ) {\frac {1}{\sqrt {- \left ( y \left ( x \right ) \right ) ^{2}+ \left ( 2\,a+{\it \_C1} \right ) y \left ( x \right ) -a \left ( {\it \_C1}+a \right ) }}}} \right ) a+{\frac {{\it \_C1}}{2}\arctan \left ( {1 \left ( y \left ( x \right ) -a-{\frac {{\it \_C1}}{2}} \right ) {\frac {1}{\sqrt {- \left ( y \left ( x \right ) \right ) ^{2}+ \left ( 2\,a+{\it \_C1} \right ) y \left ( x \right ) -a \left ( {\it \_C1}+a \right ) }}}} \right ) }-a\arctan \left ( {1 \left ( y \left ( x \right ) -a-{\frac {{\it \_C1}}{2}} \right ) {\frac {1}{\sqrt {- \left ( y \left ( x \right ) \right ) ^{2}+ \left ( 2\,a+{\it \_C1} \right ) y \left ( x \right ) +a \left ( -{\it \_C1}-a \right ) }}}} \right ) -x-{\it \_C2}=0,\sqrt {- \left ( y \left ( x \right ) \right ) ^{2}+ \left ( 2\,a+{\it \_C1} \right ) y \left ( x \right ) -a \left ( {\it \_C1}+a \right ) }-\arctan \left ( {1 \left ( y \left ( x \right ) -a-{\frac {{\it \_C1}}{2}} \right ) {\frac {1}{\sqrt {- \left ( y \left ( x \right ) \right ) ^{2}+ \left ( 2\,a+{\it \_C1} \right ) y \left ( x \right ) -a \left ( {\it \_C1}+a \right ) }}}} \right ) a-{\frac {{\it \_C1}}{2}\arctan \left ( {1 \left ( y \left ( x \right ) -a-{\frac {{\it \_C1}}{2}} \right ) {\frac {1}{\sqrt {- \left ( y \left ( x \right ) \right ) ^{2}+ \left ( 2\,a+{\it \_C1} \right ) y \left ( x \right ) -a \left ( {\it \_C1}+a \right ) }}}} \right ) }+a\arctan \left ( {1 \left ( y \left ( x \right ) -a-{\frac {{\it \_C1}}{2}} \right ) {\frac {1}{\sqrt {- \left ( y \left ( x \right ) \right ) ^{2}+ \left ( 2\,a+{\it \_C1} \right ) y \left ( x \right ) +a \left ( -{\it \_C1}-a \right ) }}}} \right ) -x-{\it \_C2}=0 \right \} \]