Answer
$870$
Work Step by Step
$a=-40$
$d=14$
$n=15$
$S_{n}=\dfrac {n}{2}\left( 2a+\left( n-1\right) d\right) =\dfrac {15}{2}\left( -80+\left( 15-1\right) \times 14\right) =\dfrac {15}{2}\times 116=870$
Precalculus: Mathematics for Calculus, 7th Edition
by Stewart, James; Redlin, Lothar; Watson, Saleem
Published by
Brooks Cole
ISBN 10:
1305071751
ISBN 13:
978-1-30507-175-9
Chapter 12 - Section 12.2 - Arithmetic Sequences - 12.2 Exercises - Page 857: 53
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