2.2.6.4 ✓ Mathematica. Time used: 0.02 (sec). Leaf size: 22

ode=D[x[t],{t,2}]-4*D[x[t],t]+5*x[t]==0; 
ic={}; 
DSolve[{ode,ic},x[t],t,IncludeSingularSolutions->True]
 

\begin{align*} x(t)&\to e^{2 t} (c_2 \cos (t)+c_1 \sin (t)) \end{align*}