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: 37

Answer

$2.5$

Work Step by Step

$a_{m}-a_{n}=\left( m-n\right) d\Rightarrow a_{20}-a_{7}=\left( 20-7\right) d\Rightarrow 69-23.5=13d\Rightarrow d=3.5\Rightarrow a_{7}=a_{1}+6d\Rightarrow 23.5=a_{1}+6\times 3.5\Rightarrow a_{1}=2.5$
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