\[ y^{(3)}(x)-\lambda y(x)=0 \] ✓ Mathematica : cpu = 0.0066122 (sec), leaf count = 53
DSolve[-(lambda*y[x]) + Derivative[3][y][x] == 0,y[x],x]
\[\left \{\left \{y(x)\to c_1 e^{(-1)^{2/3} \sqrt [3]{\lambda } x}+c_2 e^{-\sqrt [3]{-1} \sqrt [3]{\lambda } x}+c_3 e^{\sqrt [3]{\lambda } x}\right \}\right \}\] ✓ Maple : cpu = 0.025 (sec), leaf count = 47
dsolve(diff(diff(diff(y(x),x),x),x)-lambda*y(x)=0,y(x))
\[y \left (x \right ) = c_{1} {\mathrm e}^{-\frac {\lambda ^{\frac {1}{3}} \left (1+i \sqrt {3}\right ) x}{2}}+c_{2} {\mathrm e}^{\frac {\lambda ^{\frac {1}{3}} \left (i \sqrt {3}-1\right ) x}{2}}+c_{3} {\mathrm e}^{\lambda ^{\frac {1}{3}} x}\]