\[ y''(x)=0 \] ✓ Mathematica : cpu = 0.003507 (sec), leaf count = 12
\[\{\{y(x)\to c_2 x+c_1\}\}\] ✓ Maple : cpu = 0.004 (sec), leaf count = 9
\[\{y \left (x \right ) = c_{1} x +c_{2}\}\]
\[ y^{\prime \prime }=0 \]
Integration twice gives
\[ y\left ( x\right ) =c_{1}x+c_{2}\]