$$\left. \begin{array} { l } { a = 8 , a _ { n } = 62 S _ { n } = 2 } \\ { a _ { n } = 4 , d = 2 S _ { n } = - 14 } \\ { a = 3 , n = 8 S = 192 } \\ { I - \right.$$
$a=8$
$a_{n}=62S_{n}$
$S_{n}\in \mathrm{R}$
