[[_high_order, _linear, _nonhomogeneous]]
Book solution method
TO DO
Mathematica ✓
cpu = 0.066143 (sec), leaf count = 38
Maple ✓
cpu = 0.096 (sec), leaf count = 31
DSolve[y''''[x] == E^x*Cos[x] + y[x],y[x],x]
Mathematica raw output
{{y[x] -> E^x*C[1] + C[3]/E^x + (-E^x/5 + C[2])*Cos[x] + C[4]*Sin[x]}}
Maple raw input
dsolve(diff(diff(diff(diff(y(x),x),x),x),x) = y(x)+exp(x)*cos(x), y(x),'implicit')
Maple raw output
y(x) = _C4*exp(-x)+1/5*(5*_C1-exp(x))*cos(x)+_C2*exp(x)+_C3*sin(x)