$\mathscr{L}$ 를 라플라스 변환(Laplace transform)이라 할 때, $\displaystyle \mathscr{L} \left (\frac{e ^ {t} -e ^ {-t}} {t} \right)$ 는?

• ①$\displaystyle e ^ {\frac{s+1} {s-1}}$
• ②$\displaystyle e ^ {\frac{s-1} {s+1}}$
• ③$\displaystyle \ln \left | \frac{s+1} {s-1} \right |$
• ④$\displaystyle \ln \left | \frac{s-1} {s+1} \right |$