Answer
Formula for $a_{n}$ term of the given sequence = $a_{1}$ + (n - 1) d.
Where
$a_{1}$ = first term
d = Common difference
n = $n^{th}$ number of term
$20^{th}$ term of sequence = - 69
Work Step by Step
Given arithmetic sequence = 7, 3, -1, -5- - - - -
Common difference between consecutive term d = (-5) - (-1) = (-1)- 3 = 3 - 7 = (-4).
Formula for $a_{n}$ term of the given sequence = $a_{1}$ + (n - 1) d.
Where
$a_{1}$ = first term
d = Common difference
n = $n^{th}$ number of term
$20^{th}$ term of sequence = 7 + (20 - 1) $\times$ (-4)
= 7 + 19$\times$(-4)
= 7 - 76
= - 69
