Answer:
20th term = [tex]-59[/tex]
Step-by-step explanation:
An arithmetic sequence has the formula
[tex]a_n = a_1 + d(n - 1)[/tex]
where
[tex]a_n $ is the nth term\\a_1 = $ first term\\d = common difference[/tex]
Given the sequence 17, 13, 9, ... we see
[tex]a_1 = 17\\d = -4[/tex]
and we are asked to find the 20th term so n = 20
Using the formula:
[tex]a_{20} = 17 + (-4)(20-1)\\\\a_{20} = 17 + - 4 (19)\\\\a_{20} = 17 - 76\\\\a_{20} = -59[/tex]