Answer
$225$
Work Step by Step
We need to use the formula $ a_n =a_1+(n-1) d $
Here, $ a_1=-6$ and $ d=3$
$ a_{15}=-6 +(15-1) \times (3) =36$
or, $ a_{15}=36$
Now, $ S_{15}=\dfrac{15(-6+36)}{2}=225$
Precalculus (6th Edition) Blitzer
by Blitzer, Robert F.
Published by
Pearson
ISBN 10:
0-13446-914-3
ISBN 13:
978-0-13446-914-0
Chapter 10 - Review Exercises - Page 1124: 23
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