## College Algebra (10th Edition)

$d(D, E) = 2$
$d(D, E)$ represents the distance between the points D and E on a number line. If the coordinates of D and E are $d$ and $e$, respectively, then: $d(D, E) = |d-e|$ Based on the given number line, the coordinates of D and E are 1 and $3$, respectively. Use the formula above to obtain: $d(D, E) = |1-3| = |-2| =2$ Thus, $d(D, E) = 2$