Answer
General Formula: $a_n=9+(n-1)(2)$
$a_{20}=47$
Work Step by Step
The formula for the general term (the nth term) of an arithmetic sequence is:
$a_n=a_1+(n−1)d$
where
d = common difference
$a_1$ = first term
$a_n$ = nth term
n = term number
The given arithmetic sequence has:
$a_1=9$ and $d=2$
Substitute these into the given formula above:
$a_n = 9 + (n-1)(2)$
Thus,
$a_{20} = 9+(20-1)(2)
\\a_{20}=9+19(2)
\\a_{20}=9+38
\\a_{20}=47$
