Answer
$-2$
Work Step by Step
Given that $
a_n=-\dfrac{n}{3}
$ then the first 3 terms are
\begin{array}{l}
a_1=-\dfrac{1}{3}
,\\\\
a_2=-\dfrac{2}{3}
,\\\\
a_3=-\dfrac{3}{3}\\
a_3=-1
.\end{array}
Hence, the sum is $
-\dfrac{1}{3}-\dfrac{2}{3}-1
=
-2
.$
