Given A.P. Series: –1, 4, 9, 14, ......
Since the series is an A.P. series hence between every consecutive terms there is a common difference (d)
We know that the nth term in an A.P. series is given by
tn = a + (n–1)d
tn : Represents the nth term of an A.P.
a : Represents the first term of the A.P. series
d : Represents the common difference
n : Represents the position of nth term of the A.P.
So according to the problem:
129 = -1 + (n-1) × 5
⇒ 130 = (n-1) × 5
⇒ n-1 = 26
Answer: The value of n = 27
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