Algebra 2 (1st Edition)

Published by McDougal Littell
ISBN 10: 0618595414
ISBN 13: 978-0-61859-541-9

Chapter 12 Sequences and Series - 12.2 Analyze Arithmetic Sequences and Series - Guided Practice for Examples 2, 3, and 4 - Page 804: 2


$a_{n}=20-3n$ $a_{20}=-40$

Work Step by Step

The sequence is arithmetic, because there is a common difference between terms, $d=-3,\quad a_{1}=17.$ Write the general rule $ a_{n}=a_{1}+(n-1)d\qquad$ ... substitite $a_{1}$ and $d$ $ a_{n}=17+(n-1)(-3)\qquad$ ... simplify $a_{n}=17-3n+3$ $a_{n}=20-3n$ For n=20, $a_{20}=20-3(20)=-40$
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