\[ y'(x)-\tan (x y(x))=0 \] ✗ Mathematica : cpu = 40.3927 (sec), leaf count = 0 , could not solve
DSolve[-Tan[x*y[x]] + Derivative[1][y][x] == 0, y[x], x]
✓ Maple : cpu = 0.45 (sec), leaf count = 44
\[ \left \{ y \left ( x \right ) =-i{\it RootOf} \left ( \sqrt {2}{\it \_C1}-{\it Erf} \left ( {\frac { \left ( -x+{\it \_Z} \right ) \sqrt {2}}{2}} \right ) \sqrt {\pi }-\sqrt {\pi }{\it Erf} \left ( {\frac {\sqrt {2} \left ( x+{\it \_Z} \right ) }{2}} \right ) \right ) \right \} \]