Answer
In order for a sequence to be arithmetic, the difference of all consecutive terms must be constant.
Hence here: $a_{n+1}-a_n=((n+1)+4)-(n+4)=(n+5)-(n+4)=1$, thus it is an arithmetic sequence.
$a_1=5$
$a_2=6$
$a_3=7$
$a_4=8$
Work Step by Step
In order for a sequence to be arithmetic, the difference of all consecutive terms must be constant.
Hence here: $a_{n+1}-a_n=((n+1)+4)-(n+4)=(n+5)-(n+4)=1$, thus it is an arithmetic sequence.
$a_1=1+4=5$
$a_2=2+4=6$
$a_3=3+4=7$
$a_4=4+4=8$
