Answer
$n=33$
Work Step by Step
$a_n=-5n^2+40$ when $a_n=-5405$
$-5n^2+40=-5405$
$\implies -5n^2=-5445$
$\implies n^2=1089$
$\implies n=\sqrt{1089}=33$
Intermediate Algebra: Connecting Concepts through Application
by Clark, Mark; Anfinson, Cynthia
Published by
Brooks Cole
ISBN 10:
0-53449-636-9
ISBN 13:
978-0-53449-636-4
Chapter 9 - Conic Sections, Sequences, and Series - 9.3 Arithmetic Sequences - 9.3 Exercises - Page 727: 18
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