Here's the solution,
we know,
[tex] \large \boxed{Sn = \frac{n}{2}[ 2a _1 + (n - 1)d ] }[/tex]
=》
[tex]Sn = \dfrac{17}{2} [ (2 \times 8 )+ (17 - 1) \times ( - 9) ][/tex]
=》
[tex]Sn = \dfrac{17}{2} [16 + (16 \times - 9)][/tex]
=》
[tex]Sn = \dfrac{17}{2} [16 + ( - 144)][/tex]
=》
[tex]Sn = \dfrac{17}{2} \times (- 128)[/tex]
=》
[tex]Sn = 17 \times ( - 64)[/tex]
=》
[tex]\huge\boxed{Sn = - 1088}[/tex]
