Answer
General Formula: $a_n=-20+(n-1)(-4)$
$a_{20}=-96$
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:
$a_1=-20$ and $d=-4$
Substitute these into the given formula above:
$a_n = -20+ (n-1)(-4)$
Thus,
$a_{20} = -20+(20-1)(-4)
\\a_{20}=-20+19(-4)
\\a_{20}=-20+(-76)
\\a_{20}=-96$
