t=var('t')
y1=function('y1',t)
deq=diff(y1,t,2)+2*diff(y1,t,1)+y1-e^t==0
desolve(deq,[y1,t])
y2=function('y2',t)
deq1=diff(y2,t,1)+desolve(deq,[y1,t])-e^t==0
desolve(deq1,[y2,t])