\[ a y(x)^2-b \cos (c+x)+y(x) y'(x)=0 \] ✓ Mathematica : cpu = 0.0718223 (sec), leaf count = 118
\[\left \{\left \{y(x)\to -\frac {\sqrt {4 a^2 c_1 e^{-2 a x}+4 a b \cos (c+x)+c_1 e^{-2 a x}+2 b \sin (c+x)}}{\sqrt {4 a^2+1}}\right \},\left \{y(x)\to \frac {\sqrt {4 a^2 c_1 e^{-2 a x}+4 a b \cos (c+x)+c_1 e^{-2 a x}+2 b \sin (c+x)}}{\sqrt {4 a^2+1}}\right \}\right \}\]
✓ Maple : cpu = 0.069 (sec), leaf count = 116
\[ \left \{ y \left ( x \right ) ={\frac {1}{4\,{a}^{2}+1}\sqrt { \left ( 4\,{a}^{2}+1 \right ) \left ( 4\,{{\rm e}^{-2\,ax}}{\it \_C1}\,{a}^{2}+4\,\cos \left ( x+c \right ) ab+{{\rm e}^{-2\,ax}}{\it \_C1}+2\,\sin \left ( x+c \right ) b \right ) }},y \left ( x \right ) =-{\frac {1}{4\,{a}^{2}+1}\sqrt { \left ( 4\,{a}^{2}+1 \right ) \left ( 4\,{{\rm e}^{-2\,ax}}{\it \_C1}\,{a}^{2}+4\,\cos \left ( x+c \right ) ab+{{\rm e}^{-2\,ax}}{\it \_C1}+2\,\sin \left ( x+c \right ) b \right ) }} \right \} \]