## College Algebra (11th Edition)

$d=-4$
$\bf{\text{Solution Outline:}}$ To find the common difference of the given arithmetic sequence, $-8,-12,-16,-20,... ,$ subtract a term by its previous term. $\bf{\text{Solution Details:}}$ Since the common difference of an arithmetic sequence is the difference between a term and its previous term, then with $a_2= -12$ and $a_1= -8$, the common difference, $d$, is \begin{array}{l}\require{cancel} d=-12-(-8) \\\\ d=-12+8 \\\\ d=-4 .\end{array}