\[ \boxed { \left ( a-b \right ) \left ( y \left ( x \right ) \right ) ^{2} \left ( {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) \right ) ^{2}-2\,bxy \left ( x \right ) {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) +a \left ( y \left ( x \right ) \right ) ^{2}-b{x}^{2}-ab=0} \]
Mathematica: cpu = 1.322668 (sec), leaf count = 100 \[ \left \{\left \{y(x)\to -\frac {\sqrt {-a b-2 a c_1 x+a c_1^2+a x^2+b^2-b x^2}}{\sqrt {b-a}}\right \},\left \{y(x)\to \frac {\sqrt {-a b-2 a c_1 x+a c_1^2+a x^2+b^2-b x^2}}{\sqrt {b-a}}\right \}\right \} \]
Maple: cpu = 1.232 (sec), leaf count = 260 \[ \left \{ y \left ( x \right ) ={\frac {1}{b}\sqrt {-{\it \_C1}\,ab+{\it \_C1}\,{b}^{2}-{b}^{2}{x}^{2}-2\,b\sqrt {{\it \_C1}\,ab-a{b}^{2}}x+a{b }^{2}}},y \left ( x \right ) ={\frac {1}{b}\sqrt {-{\it \_C1}\,ab+{\it \_C1}\,{b}^{2}-{b}^{2}{x}^{2}+2\,b\sqrt {{\it \_C1}\,ab-a{b}^{2}}x+a{b }^{2}}},y \left ( x \right ) ={\frac {1}{a-b}\sqrt { \left ( a-b \right ) b \left ( {x}^{2}+a-b \right ) }},y \left ( x \right ) =-{\frac {1}{b} \sqrt {-{\it \_C1}\,ab+{\it \_C1}\,{b}^{2}-{b}^{2}{x}^{2}-2\,b\sqrt {{ \it \_C1}\,ab-a{b}^{2}}x+a{b}^{2}}},y \left ( x \right ) =-{\frac {1}{b} \sqrt {-{\it \_C1}\,ab+{\it \_C1}\,{b}^{2}-{b}^{2}{x}^{2}+2\,b\sqrt {{ \it \_C1}\,ab-a{b}^{2}}x+a{b}^{2}}},y \left ( x \right ) =-{\frac {1}{a- b}\sqrt { \left ( a-b \right ) b \left ( {x}^{2}+a-b \right ) }} \right \} \]