## College Algebra (6th Edition)

$S_{n}$ = $\frac{n}{2}$($a_{1}$ + $a_{n}$) $a_{1}$ is the first term, $a_{n}$ is the last term $a_{n}$ = $a_{1}$ + (n - 1) d
The sum $S_{n}$ = $\frac{n}{2}$($a_{1}$ + $a_{n}$) Where $a_{1}$ is the first term, and $a_{n}$ is the last term $a_{n}$ = $a_{1}$ + (n - 1) d