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Arithmetic Progressions
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02/06/2021 11:07 am
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Which term of the AP: 121, 117, 113, . . ., is its first negative term? [Hint: Find n for an < 0]
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02/06/2021 11:09 am
Given the AP series is 121, 117, 113, . . .,
Thus, first term, a = 121
Common difference, d = 117-121= -4
an = a+(n −1)d
Therefore,
an = 121+(n−1)(-4)
= 121-4n+4
=125-4n
To find the first negative term of the series, an < 0
125 - 4n < 0
125 < 4n
n > 125/4
n > 31.25
Therefore, the first negative term of the series is 32nd term.