Answer
$S_{5} =-25$
Work Step by Step
Sum of the first five negative odd integers.
Sequence
$-1,-3,-5,-7,-9$ is an arithmetic sequence
$a_{1} = -1$
$a_{n} = -9$
To find sum of first five terms, substitute $a_{1},a_{n} $ and $n=5$ in
$S_{n} = \frac{n}{2} (a_{1}+a_{n}) $
$S_{5} = \frac{5}{2} (-1-9) $
$S_{5} = \frac{5}{2} (-10) $
$S_{5} =-25$