\[ \boxed { xy \left ( x \right ) {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) - \left ( y \left ( x \right ) \right ) ^{2}+a{x}^{3}\cos \left ( x \right ) =0} \]
Mathematica: cpu = 0.024503 (sec), leaf count = 38 \[ \left \{\left \{y(x)\to -x \sqrt {c_1-2 a \sin (x)}\right \},\left \{y(x)\to x \sqrt {c_1-2 a \sin (x)}\right \}\right \} \]
Maple: cpu = 0.031 (sec), leaf count = 30 \[ \left \{ y \left ( x \right ) =\sqrt {-2\,a\sin \left ( x \right ) +{\it \_C1}}x,y \left ( x \right ) =-\sqrt {-2\,a\sin \left ( x \right ) +{\it \_C1}}x \right \} \]