Answer
$63$
Work Step by Step
We know that the general formula of an arithmetic sequence is given by
$a_n= a_1+(n-1) d$
Here, $a_n=3+2(n-1) $
$a_n=2n+1$
When $n=7$, then we have
$a_7=(2)(7)+1=15$
Thus, we have $S_n=\dfrac{7(3+15)}{2}=63$
Algebra 2 (1st Edition)
by Larson, Ron; Boswell, Laurie; Kanold, Timothy D.; Stiff, Lee
Published by
McDougal Littell
ISBN 10:
0618595414
ISBN 13:
978-0-61859-541-9
Chapter 12 Sequences and Series - 12.2 Analyze Arithmetic Sequences and Series - 12.2 Exercises - Problem Solving - Page 808: 64
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