Answer
The first four terms.
$2, 0,-2,-4$
and a common difference of $-2$.
Work Step by Step
We need to substitute $1, 2, 3,$ and $4$ for $n$ into the given equation to find the first four terms.
$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 $
We can see that the common difference is $-2$ (decreases by $2$ each time). Thus, the sequence is arithmetic with a common difference of $-2$.
