Chapter 9 - Section 9.2 - Arithmetic Sequences - 9.2 Assess Your Understanding - Page 654: 12

common difference = $-2$ The first four terms are: $2, 0, -2, -4$

To find the first four terms, substitute $1, 2, 3, 4$ for $n$ in the given formula. $a_1 = 4-2(1) = 4-2= 2$ $a_2= 4-2(2) =4-4=0$ $a_3 = 4-2(3)=4-6=-2$ $a_4 = 4-2(4) = 4-8 = -4$ The terms decrease by $2$ units, so the sequence is arithmetic with a common difference of $-2$.