1. The problem statement, all variables and given/known data y'' + y = delta(t-2*pi) 3. The attempt at a solution I have solved this using laplace transforms. Y = e^(-2*pi*s)/(s^2 + 1) + 10s/(s^2 + 1) so that y = sint*u(t - 2*pi) + 10 *cost what I don't understand is this function is not definied for t<0. According to my book, the answer is: y = 10 cos t if 0<t<2*pi and y = 10cost + sint if t>2*pi Why is this?