Of $\displaystyle \frac{1}{4s^{2}-8s}$
I am approaching the partial fraction $$\displaystyle \frac{1}{4s\left(s-2\right)}=\frac{A}{4s}+\frac{B}{s-2},\text{ where }A=-\frac{1}{2},B=\frac{1}{8}$$
Memorizing the table, I have $$\displaystyle f(t)=-\frac{1}{8}+\frac{1}{8}e^{2t}$$
However, the answer seems to be $$\displaystyle \frac{1}{4}e^{t}\sinh{t}$$
How come?
$$\frac{1}{4}e^{t}\sinh{(t)} = \frac{1}{4}e^{t}\left(\frac{e^t - e^{-t}}{2}\right)= \frac{e^{2t}}{8} -\frac{1}{8} \\$$
So both the book and you are correct.