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: 25

Answer

$a_n=152-14n$

Work Step by Step

Let $a_n$ be our arithmetic sequence. We are given: $$\begin{align*} a_4&=96\\ d&=-14. \end{align*}$$ We determine the first term $a_1$: $$\begin{align*} a_n&=a_1+(n-1)d\\ a_4&=a_1+(4-1)d\\ 96&=a_1+3(-14)\\ 96+42&=a_1\\ a_1&=138. \end{align*}$$ We write the rule for the general term $a_n$: $$\begin{align*} a_n&=a_1+(n-1)d\\ a_n&=138+(n-1)(-14)=138-14n+14=152-14n. \end{align*}$$ We got: $$a_n=152-14n.\tag1$$ We calculate the first six terms substituting $n=2,3,5,6$ in Eq. $(1)$ and $a_1=138$, $a_4=96$: $$\begin{align*} a_1&=138\\ a_2&=152-14(2)=124\\ a_3&=152-14(3)=110\\ a_4&=96\\ a_5&=152-14(5)=82\\ a_6&=152-14(6)=68. \end{align*}$$ Graph the first six terms:
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