Use the method $of$ variation $of$ parameters $to$ show that:

$y(t)=c_{1}cos(t)+c_{2}sin(t)+{\displaystyle \underset{0}{\overset{t}{}}}f(s)sin(t-s)ds$

$Is$ a general solution $to$ the differential equations:

$y^{\text{'}\text{'}}+y=f(t)$

Where $f(t)is$ a continuous function $on(-,)$

Hint: Use the identity $sin(t-s)=sin(t)cos(s)-sin(s)cos(t)$