\[ \lambda y(x)+y^{(4)}(x)=0 \] ✓ Mathematica : cpu = 0.0041609 (sec), leaf count = 76
\[\left \{\left \{y(x)\to c_1 e^{(-1)^{3/4} \sqrt [4]{\lambda } x}+c_2 e^{-\sqrt [4]{-1} \sqrt [4]{\lambda } x}+c_3 e^{-(-1)^{3/4} \sqrt [4]{\lambda } x}+c_4 e^{\sqrt [4]{-1} \sqrt [4]{\lambda } x}\right \}\right \}\] ✓ Maple : cpu = 0.02 (sec), leaf count = 50
\[y \relax (x ) = c_{1} {\mathrm e}^{-i \left (-\lambda \right )^{\frac {1}{4}} x}+c_{2} {\mathrm e}^{i \left (-\lambda \right )^{\frac {1}{4}} x}+c_{3} {\mathrm e}^{-\left (-\lambda \right )^{\frac {1}{4}} x}+c_{4} {\mathrm e}^{\left (-\lambda \right )^{\frac {1}{4}} x}\]