함수 $\displaystyle F \left (s \right) = \frac{s} {\left (s^2 +4 \right) \left (s+2 \right)}$ 의 역라플라스변환(inverse Laplace transform)은?

• ①$\cos 2t- \sin 2t-e^ {-2t}$
• ②$\displaystyle \frac{1} {2} \left (\cos 2t+ \sin 2t-e^ {-2t} \right)$
• ③$\displaystyle \frac{1} {3} \left (\cos 2t- \sin 2t-e^ {-2t} \right)$
• ④$\displaystyle \frac{1} {4} \left (\cos 2t+ \sin 2t-e^ {-2t} \right)$