How to solve and plot a 2nd oder differenetial equation?

i have already done the solving part but i am stuck on the plotting.Here is the question

Find a 2 pi periodic solution to the equation x''+2x'+x=cos(t)

Also find the solution to x''+2x'+x=cos(t), x(0)=x'(0)=0

and verify that it approaches the periodic solution as t grows

Here is what i wrote on matlab

syms t xt

xt=dsolve('D2x+2*Dx+1*x=cos(t)','x(0)=Dx(0)=0')

please help for the question and the plot if it has to be between time period / limits

[Star Strider]

Use the fplot function.