## College Algebra (11th Edition)

$a_8=19 \text{ and } a_n=3+2n$
$\bf{\text{Solution Outline:}}$ To find $a_8$ and $a_n$ in the given sequence \begin{array}{l}\require{cancel} 5,7,9,... ,\end{array} use the formula for finding the $n$th term of an arithmetic sequence. $\bf{\text{Solution Details:}}$ Since the common difference, $d,$ is the difference between a term and the term preceeding it, then \begin{array}{l}\require{cancel} d=a_2-a_1 \\\\ d=7-5 \\\\ d=2 ,\end{array} Using $a_n=a_1+(n-1)d$ with $a_1=5$ and $d=2$ then \begin{array}{l}\require{cancel} a_n=5+(n-1)(2) \\\\ a_n=5+2n-2 \\\\ a_n=3+2n .\end{array} With $n=8,$ then \begin{array}{l}\require{cancel} a_8=3+2(8) \\\\ a_8=3+16 \\\\ a_8=19 .\end{array} Hence, $a_8=19 \text{ and } a_n=3+2n .$