\[ \sqrt {y(x)} y''(x)-a=0 \] ✓ Mathematica : cpu = 0.074181 (sec), leaf count = 1677
\[\left \{\left \{y(x)\to \frac {3 c_1{}^2}{16 a^2}+\frac {\sqrt [3]{-\frac {221184 c_1{}^6}{a^6}+\frac {159252480 x^2 c_1{}^3}{a^2}+\frac {159252480 c_2{}^2 c_1{}^3}{a^2}+\frac {318504960 x c_2 c_1{}^3}{a^2}+2293235712 a^2 x^4+2293235712 a^2 c_2{}^4+9172942848 a^2 x c_2{}^3+13759414272 a^2 x^2 c_2{}^2+9172942848 a^2 x^3 c_2+\sqrt {4 \left (-\frac {2304 c_1{}^4}{a^4}-663552 x^2 c_1-663552 c_2{}^2 c_1-1327104 x c_2 c_1\right ){}^3+\left (-\frac {221184 c_1{}^6}{a^6}+\frac {159252480 x^2 c_1{}^3}{a^2}+\frac {159252480 c_2{}^2 c_1{}^3}{a^2}+\frac {318504960 x c_2 c_1{}^3}{a^2}+2293235712 a^2 x^4+2293235712 a^2 c_2{}^4+9172942848 a^2 x c_2{}^3+13759414272 a^2 x^2 c_2{}^2+9172942848 a^2 x^3 c_2\right ){}^2}}}{768 \sqrt [3]{2}}-\frac {-\frac {2304 c_1{}^4}{a^4}-663552 x^2 c_1-663552 c_2{}^2 c_1-1327104 x c_2 c_1}{384\ 2^{2/3} \sqrt [3]{-\frac {221184 c_1{}^6}{a^6}+\frac {159252480 x^2 c_1{}^3}{a^2}+\frac {159252480 c_2{}^2 c_1{}^3}{a^2}+\frac {318504960 x c_2 c_1{}^3}{a^2}+2293235712 a^2 x^4+2293235712 a^2 c_2{}^4+9172942848 a^2 x c_2{}^3+13759414272 a^2 x^2 c_2{}^2+9172942848 a^2 x^3 c_2+\sqrt {4 \left (-\frac {2304 c_1{}^4}{a^4}-663552 x^2 c_1-663552 c_2{}^2 c_1-1327104 x c_2 c_1\right ){}^3+\left (-\frac {221184 c_1{}^6}{a^6}+\frac {159252480 x^2 c_1{}^3}{a^2}+\frac {159252480 c_2{}^2 c_1{}^3}{a^2}+\frac {318504960 x c_2 c_1{}^3}{a^2}+2293235712 a^2 x^4+2293235712 a^2 c_2{}^4+9172942848 a^2 x c_2{}^3+13759414272 a^2 x^2 c_2{}^2+9172942848 a^2 x^3 c_2\right ){}^2}}}\right \},\left \{y(x)\to \frac {3 c_1{}^2}{16 a^2}-\frac {\left (1-i \sqrt {3}\right ) \sqrt [3]{-\frac {221184 c_1{}^6}{a^6}+\frac {159252480 x^2 c_1{}^3}{a^2}+\frac {159252480 c_2{}^2 c_1{}^3}{a^2}+\frac {318504960 x c_2 c_1{}^3}{a^2}+2293235712 a^2 x^4+2293235712 a^2 c_2{}^4+9172942848 a^2 x c_2{}^3+13759414272 a^2 x^2 c_2{}^2+9172942848 a^2 x^3 c_2+\sqrt {4 \left (-\frac {2304 c_1{}^4}{a^4}-663552 x^2 c_1-663552 c_2{}^2 c_1-1327104 x c_2 c_1\right ){}^3+\left (-\frac {221184 c_1{}^6}{a^6}+\frac {159252480 x^2 c_1{}^3}{a^2}+\frac {159252480 c_2{}^2 c_1{}^3}{a^2}+\frac {318504960 x c_2 c_1{}^3}{a^2}+2293235712 a^2 x^4+2293235712 a^2 c_2{}^4+9172942848 a^2 x c_2{}^3+13759414272 a^2 x^2 c_2{}^2+9172942848 a^2 x^3 c_2\right ){}^2}}}{1536 \sqrt [3]{2}}+\frac {\left (1+i \sqrt {3}\right ) \left (-\frac {2304 c_1{}^4}{a^4}-663552 x^2 c_1-663552 c_2{}^2 c_1-1327104 x c_2 c_1\right )}{768\ 2^{2/3} \sqrt [3]{-\frac {221184 c_1{}^6}{a^6}+\frac {159252480 x^2 c_1{}^3}{a^2}+\frac {159252480 c_2{}^2 c_1{}^3}{a^2}+\frac {318504960 x c_2 c_1{}^3}{a^2}+2293235712 a^2 x^4+2293235712 a^2 c_2{}^4+9172942848 a^2 x c_2{}^3+13759414272 a^2 x^2 c_2{}^2+9172942848 a^2 x^3 c_2+\sqrt {4 \left (-\frac {2304 c_1{}^4}{a^4}-663552 x^2 c_1-663552 c_2{}^2 c_1-1327104 x c_2 c_1\right ){}^3+\left (-\frac {221184 c_1{}^6}{a^6}+\frac {159252480 x^2 c_1{}^3}{a^2}+\frac {159252480 c_2{}^2 c_1{}^3}{a^2}+\frac {318504960 x c_2 c_1{}^3}{a^2}+2293235712 a^2 x^4+2293235712 a^2 c_2{}^4+9172942848 a^2 x c_2{}^3+13759414272 a^2 x^2 c_2{}^2+9172942848 a^2 x^3 c_2\right ){}^2}}}\right \},\left \{y(x)\to \frac {3 c_1{}^2}{16 a^2}-\frac {\left (1+i \sqrt {3}\right ) \sqrt [3]{-\frac {221184 c_1{}^6}{a^6}+\frac {159252480 x^2 c_1{}^3}{a^2}+\frac {159252480 c_2{}^2 c_1{}^3}{a^2}+\frac {318504960 x c_2 c_1{}^3}{a^2}+2293235712 a^2 x^4+2293235712 a^2 c_2{}^4+9172942848 a^2 x c_2{}^3+13759414272 a^2 x^2 c_2{}^2+9172942848 a^2 x^3 c_2+\sqrt {4 \left (-\frac {2304 c_1{}^4}{a^4}-663552 x^2 c_1-663552 c_2{}^2 c_1-1327104 x c_2 c_1\right ){}^3+\left (-\frac {221184 c_1{}^6}{a^6}+\frac {159252480 x^2 c_1{}^3}{a^2}+\frac {159252480 c_2{}^2 c_1{}^3}{a^2}+\frac {318504960 x c_2 c_1{}^3}{a^2}+2293235712 a^2 x^4+2293235712 a^2 c_2{}^4+9172942848 a^2 x c_2{}^3+13759414272 a^2 x^2 c_2{}^2+9172942848 a^2 x^3 c_2\right ){}^2}}}{1536 \sqrt [3]{2}}+\frac {\left (1-i \sqrt {3}\right ) \left (-\frac {2304 c_1{}^4}{a^4}-663552 x^2 c_1-663552 c_2{}^2 c_1-1327104 x c_2 c_1\right )}{768\ 2^{2/3} \sqrt [3]{-\frac {221184 c_1{}^6}{a^6}+\frac {159252480 x^2 c_1{}^3}{a^2}+\frac {159252480 c_2{}^2 c_1{}^3}{a^2}+\frac {318504960 x c_2 c_1{}^3}{a^2}+2293235712 a^2 x^4+2293235712 a^2 c_2{}^4+9172942848 a^2 x c_2{}^3+13759414272 a^2 x^2 c_2{}^2+9172942848 a^2 x^3 c_2+\sqrt {4 \left (-\frac {2304 c_1{}^4}{a^4}-663552 x^2 c_1-663552 c_2{}^2 c_1-1327104 x c_2 c_1\right ){}^3+\left (-\frac {221184 c_1{}^6}{a^6}+\frac {159252480 x^2 c_1{}^3}{a^2}+\frac {159252480 c_2{}^2 c_1{}^3}{a^2}+\frac {318504960 x c_2 c_1{}^3}{a^2}+2293235712 a^2 x^4+2293235712 a^2 c_2{}^4+9172942848 a^2 x c_2{}^3+13759414272 a^2 x^2 c_2{}^2+9172942848 a^2 x^3 c_2\right ){}^2}}}\right \}\right \}\] ✓ Maple : cpu = 0.542 (sec), leaf count = 91
\[ \left \{ {\frac {1}{12\,{a}^{2}} \left ( -3\,{\it \_C1}\,\sqrt {4\,a\sqrt {y \left ( x \right ) }-{\it \_C1}}- \left ( 4\,a\sqrt {y \left ( x \right ) }-{\it \_C1} \right ) ^{{\frac {3}{2}}} \right ) }-x-{\it \_C2}=0,{\frac {1}{12\,{a}^{2}} \left ( 3\,{\it \_C1}\,\sqrt {4\,a\sqrt {y \left ( x \right ) }-{\it \_C1}}+ \left ( 4\,a\sqrt {y \left ( x \right ) }-{\it \_C1} \right ) ^{{\frac {3}{2}}} \right ) }-x-{\it \_C2}=0 \right \} \]