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 - Page 1025: 36



Work Step by Step

$\left( a_{m}-a_{n}\right) =\left( m-n\right) d\Rightarrow a_{13}-a_{6}=\left( 13-6\right) d\Rightarrow 26-\left( -72\right) =7d=d=14;a_{6}=a_{1}+5d\Rightarrow -72=a_{1}+5\times 14\Rightarrow a_{1}=-142$
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