The Laplace transform of the waveform shown in the figure

The Laplace transform of the waveform shown in the figure is
1/s² (1 + Ae – s + Be – 4s + Ce – 6s + De – 8s).
The value of D is ______

ƒ(t) = t[U(t) – U(t – 1)] + 1 [U(t – 1) – U(t – 4)] + (5 – t) [U(t – 4) – U(t – 6)] + (t/2 × -4) [U(t – 6) – U(t – 8)]

F(s) =	1	[1 - e^-s] +	1	[e^-s - e^-4s] +		5	-	1		[e^-4s - e^-6s] +		4	-	1		[e^-6s - e^-8s]
	s²		s			s		s²				2s²		s

Comparing, we get D = – 0.5