1. y(t) = 2 cos(2t) + u_{pi/2}(t) [3 sin(3t) - 1/3 cos(3t)] + u_{pi}(t)exp(3(pi-t)) [cos(t) - 2 sin(t)]
2. 1. x(t) = (2+t) exp(-4t)
   2. y(t) = u_1(t) (t-1) exp(t-1)
   3. y(t) = exp(t) - 2 exp(t) - t + u_1(t) [t-1-sinh(t-1)]
   4. y(t) = 1/2 (integral from 0 to t) [sinh(t-s)-sin(t-s)]g(s)ds
3. sin(t)*sin(t) = 1/2 (sin(t)-tcos(t)) is negative when t = 2 pi, for example