\[ y''(x)=0 \] ✓ Mathematica : cpu = 0.00409388 (sec), leaf count = 12
\[\left \{\left \{y(x)\to c_2 x+c_1\right \}\right \}\]
✓ Maple : cpu = 0.006 (sec), leaf count = 9
\[ \left \{ y \left ( x \right ) ={\it \_C1}\,x+{\it \_C2} \right \} \]
\[ y^{\prime \prime }=0 \]
Integration twice gives
\[ y\left ( x\right ) =c_{1}x+c_{2}\]