\[ 3 y'(x)+y^{(3)}(x)-4 y(x)=0 \] ✓ Mathematica : cpu = 0.005238 (sec), leaf count = 54
\[\left \{\left \{y(x)\to c_3 e^x+c_2 e^{-x/2} \cos \left (\frac {\sqrt {15} x}{2}\right )+c_1 e^{-x/2} \sin \left (\frac {\sqrt {15} x}{2}\right )\right \}\right \}\] ✓ Maple : cpu = 0.007 (sec), leaf count = 35
\[ \left \{ y \left ( x \right ) ={{\rm e}^{x}}{\it \_C1}+{\it \_C2}\,{{\rm e}^{-{\frac {x}{2}}}}\sin \left ( {\frac {\sqrt {15}x}{2}} \right ) +{\it \_C3}\,{{\rm e}^{-{\frac {x}{2}}}}\cos \left ( {\frac {\sqrt {15}x}{2}} \right ) \right \} \]