t=var('t') # t represents the time
a,b,k=var('a b k')
y=function('y',t)
a=1;b=1;k=1
diffeq=diff(y,t)-a+b*cos(2*pi*t/24)+k*y
sol=desolve(diffeq,[y,t],ics=(0,2))
sol
plot(sol,(t,0,20))