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 - 12.2 Exercises - Skill Practice - Page 807: 30


$a_n=-5 +9n$

Work Step by Step

We know that the general formula of an arithmetic sequence is given by $a_n= a_1+(n-1) d$ ...(1) Here, we have $a_{4}=31$ $a_{10}=a_4+6d=85$ This gives: $d=9$ $a_1=a_4-3d=31 -3 \times 9=4$ Now, $a_n=4+(n-1)9=-5+9n$ Hence, our answer is $a_n=-5 +9n$
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