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 806: 24

Answer

$a_n=9n-70$

Work Step by Step

Let $a_n$ be our arithmetic sequence. We are given: $$\begin{align*} a_6&=-16\\ d&=9. \end{align*}$$ We determine the first term $a_1$: $$\begin{align*} a_n&=a_1+(n-1)d\\ a_6&=a_1+(6-1)d\\ -16&=a_1+5(9)\\ -16-45&=a_1\\ a_1&=-61. \end{align*}$$ We write the rule for the general term $a_n$: $$\begin{align*} a_n&=a_1+(n-1)d\\ a_n&=-61+(n-1)(9)=-61+9n-9=9n-70. \end{align*}$$ We got: $$a_n=9n-70.\tag1$$ We calculate the first six terms substituting $n=2,3,4,5$ in Eq. $(1)$ and $a_1=-61$, $a_6=-16$: $$\begin{align*} a_1&=-61\\ a_2&=9(2)-70=-52\\ a_3&=9(3)-70=-43\\ a_4&=9(4)-70=-34\\ a_5&=9(5)-70=-25\\ a_6&=-16. \end{align*}$$ Graph the first six terms:
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