Solution:
Given that the AP series is 121, 117, 113, . . .,
The, first term, a = 121 and,
The common difference, d = 117-121= -4
According to the nth term formula,
an = a+(n −1)d
Therefore,
an = 121+(n−1)(-4)
= 121-4n+4
=125-4n
an < 0 is used to discover the series’ initial negative term.
Therefore,
125-4n < 0
125 < 4n
n>125/4
n>31.25
As a result, the 32nd term is the series’ first negative term.