## Precalculus (6th Edition) Blitzer

$-385$
Here, $a_1=7$ and $r=-2$ $a_{10}=-7+(10-1)(-7)=-7-63=-70$ $S_{10}=\dfrac{10[ (-7)+(-70)}{2}$ $= \dfrac{10[ -7-70]}{2}$ $=5(-77)$ $=-385$