Precalculus (6th Edition)

Published by Pearson
ISBN 10: 013421742X
ISBN 13: 978-0-13421-742-0

Chapter 11 - Further Topics in Algebra - 11.2 Arithmetic Sequences and Series - 11.2 Exercises: 33

Answer

3

Work Step by Step

$a_{m}-a_{n}=\left( m-n\right) d\Rightarrow a_{15}-a_{5}=87-27=\left( 15-5\right) \times d\Rightarrow 60=10d\Rightarrow d=6\Rightarrow a_{5}=a_{1}+4d\Rightarrow 27=a_{1}+4\times 6\Rightarrow a_{1}=3$
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