Answer
$-10$
Work Step by Step
Using the given general term, $
a_n=-8+(n-1)3
,$ then,
\begin{array}{l}
a_1=-8+(1-1)3\\
a_1=-8+0\\
a_1=-8
,\\\\
a_2=-8+(2-1)3\\
a_2=-8+3\\
a_2=-5
,\\\\
a_3=-8+(3-1)3\\
a_3=-8+6\\
a_3=-2
,\\\\
a_4=-8+(4-1)3\\
a_4=-8+9\\
a_4=1
,\\\\
a_5=-8+(5-1)3\\
a_5=-8+12\\
a_5=4
.\end{array}
Hence, $
S_5=-8+(-5)+(-2)+1+4
=
-10
.$
