\[ a \cos \left (y'(x)\right )+b y'(x)+x=0 \] ✓ Mathematica : cpu = 0.0418369 (sec), leaf count = 42
\[\text {Solve}\left [\left \{y(x)=a \sin (\text {K$\$$137124})-a \text {K$\$$137124} \cos (\text {K$\$$137124})-\frac {b \text {K$\$$137124}^2}{2}+c_1,x=-a \cos (\text {K$\$$137124})-b \text {K$\$$137124}\right \},\{y(x),\text {K$\$$137124}\}\right ]\] ✓ Maple : cpu = 0.081 (sec), leaf count = 18
\[ \left \{ y \left ( x \right ) =\int \!{\it RootOf} \left ( a\cos \left ( {\it \_Z} \right ) +{\it \_Z}\,b+x \right ) \,{\rm d}x+{\it \_C1} \right \} \]