Answer
$a_2=\frac{a_1+a_3}{2}$
Work Step by Step
Since it is an arithmetic sequence, they have a common difference:
$$a_2-a_1=a_3-a_2$$
Solve for $a_2$:
$$a_2+a_2=a_3+a_1$$
$$2a_2=a_1+a_3$$
$$a_2=\frac{a_1+a_3}{2}$$
College Algebra (11th Edition)
by Lial, Margaret L.; Hornsby John; Schneider, David I.; Daniels, Callie
Published by
Pearson
ISBN 10:
0321671791
ISBN 13:
978-0-32167-179-0
Chapter 7 - Section 7.2 - Arithmetic Sequences and Series - 7.2 Exercises - Page 645: 22
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