\[ y''(x)-y(x)=0 \] ✓ Mathematica : cpu = 0.00509831 (sec), leaf count = 20
\[\left \{\left \{y(x)\to c_1 e^x+c_2 e^{-x}\right \}\right \}\]
✓ Maple : cpu = 0.007 (sec), leaf count = 15
\[ \left \{ y \left ( x \right ) ={\it \_C1}\,{{\rm e}^{x}}+{\it \_C2}\,{{\rm e}^{-x}} \right \} \]